The Jebel el Akhdar or "Green Mountain" is a limestone plateau which rises to a height of over 850 metres and extends for some 250 kilometres east of Benghazi parallel to the coast of Cyrenaica. A narrow coastal plain or "Sahel" lies between the sea and a steep escarpment which reaches a height of 500 metres. A few kilometres to the south a second, less well defined scarp rises to the plateau level, the area between the scarps being severely dissected by numerous steep sided wadis. The Jebel is composed in the main of flat lying Tertiary limestones which are soft and contain few impermeable horizons. Although the Jebel receives a comparatively high rainfall during the winter months, due to the porosity of the limestone, most of the water is lost by absorption into the underground drainage system and resurges either where it is of little use or below sea level.
During 1951-2 a British Army party, known as the "Deep Reconnaissance Unit", explored a large number of the caves and potholes that are developed on the Jebel and were responsible for finding the cave of Am Dubbussia, from which water is now being extracted to supply the new capital of el Beida. The chief aim of the Cambridge Expedition to Cyrenaica 1959 was to continue the search for water by spelaeological techniques. It was also hoped to carry out geomorphological studies, to make a collection of cave fauna and to make a study of the way of life of the local population. The Base Camp was set up at Dubbussia and exploration carried out chiefly in the coastal area between Labrach and Derna, although several excursions were made outside these limits.
In this report grid references given are derived from the Italian 1:100,000 map and in open country are inevitably subject to some error. Arabic place names are used in preference to the redundant Italian names.
|C.J.C. Whimster, B.A.||Leader and Geomorphologist|
|M.S. Money, B.A.||Geologist|
Preparations for the Expedition began during the Michaelmas Term 1958 and as a result of numerous requests and enquiries sent out during the winter months we were fortunate in obtaining sufficient financial and material aid to enable us to proceed with the project. A particularly welcome piece of help came at an early stage from the Libyan Public Development and Stabilisation Agency who solved one of our major problems by offering to lend us a landrover and to give us a large supply of petrol and oil. By May 1959 all our stores and equipment had arrived and in all some 1½ tons of goods were shipped to Benghazi later that month. Almost on the eve of our departure in June it was learned that an Italian dock strike would prevent us from sailing to Benghazi as planned. However, after much frantic reorganisation and considerable additional expense, we were able to fly to Benghazi from Rome, arriving on July 1st.
In Benghazi we were met by Mr. Goudie of the L.P.D.S.A. and thanks to his assistance and the help of his staff, in particular Mr. Millar, our equipment was cleared through the intricacies of the Libyan Customs the next day. Thus on July 3rd we left Benghazi and drove out to Am Dubbussia, where our base camp was set up and where we received a great deal of help from Mr. Tighe, the Resident Engineer. With the help of the landrover we were soon exploring the surrounding country and attempting to make local contacts, The bedouin proved to be willing giudes and generous hosts; a high proportion of caving time was spent drinking tea and making conversation and we were led to numerous potholes and springs, though some excursions, many of which seemed to have the common objectives of "chasms with the sound of running water at the bottom" were almost invariably wild goose chases.
A few weeks after our arrival in Libya, however, a severe blow was dealt to the expedition when the landrover was damaged beyond local repair in an accident on the rough track from Dubbussia to the el Gubba road. For a time at least our activities were mainly confined to the area in the vicinity of the camp. Nearby wadis were explored on foot for caves and springs, and Wadi es Seghi and Wadi Zaigh were partly surveyed and geologically mapped. A traverse was made along the bed of Wadi es Seghi, the thick vegetation and sudden waterfalls making walking, let alone levelling, a difficult process. Work was also begun on the Social Studies in the el Gubba area. After a time we were able to get lifts on Dubbussia transport and set up a series of subsidiary camps from which to continue our work.
The first of these camps was situated near Tert with the object of visiting several springs. The position of the camp was superb, on a hillside overlooking an Arab settlement and a spring, where throughout the day herds of goats would come to drink. We were chiefly concerned, however, with two other springs, Ain Umm Ammesc and Ain Tbelba, where small flows issued from caves. The first proved to have few possibilities but the second was of much more interest and a full account of this spring is given in Chapter 3. Our contortions and discomforts arising from this exploration were a great diversion for the local population. After this camp the party divided and while three members camped near el Atrun in order to complete the detailed geological study, the remainder moved camp to Benghazi where the cave of Lethe was explored. This was thought by the ancient Greeks to be an entrance to the Underworld and in more recent times has given rise to numerous legends of treacherous whirlpools and drowned frogmen, but we found it a placid and peaceful spot, investigations in our rubber dinghy unfortunately revealing no passage to Hades. The chief reason for this visit was the presence of a blind white shrimp which is found nowhere else; specimens were duly collected and the expedition returned none the worse for their immersion in the "Waters of Forgetfulness".
After a brief reunion, another two camps were set up, both on the coastal plain. One party enjoyed the hospitality of Miss Olive Brittan, chief beekeeper to the Cyrenaican Government, near Ras el Hilal where they explored various wadis for water and caves, unfortunately without success. The second party were very fortunate in being welcomed at the camp of a geologist of the Esso Standard Oil Co., Mr. Peter Howard, near Susa, and in being given transport. This enabled us to visit a most interesting cave several kilometres west of Susa which contained not only several large chambers and magnificent stalagmitic formations but also numerous inscriptions in Greek characters on the walls. No nook or cranny of the cave had been unvisited by our predecessors. From this camp at Susa we were also able to visit the saline lakes of Abraq Nota 12 kilometres west of Susa and to spend a day sounding their depth and exploring a rather dangerous cave with our rubber dinghy.
The final camp was situated in an Arab school at Lamluda by kind permission of the schoolmaster, Abdussalaam Futuri, who on this and many other occasions was of great service to us by acting as our guide, patron and interpreter. A number of first descents of potholes were made in Lamluda, the most interesting pot being Haua bu Nagela which is inhabited by thousands of bats.
Finally after the inevitable chaos of striking and clearing up camp, the Expedition set off home in mid-September, some via Tripoli and Tunisia, others via Malta and Italy, after what was certainly an enjoyable and interesting stay in Libya and, we hope, a useful one.
Although our thanks to the many people who helped the Expedition in various ways are recorded at the end of this report, special mention should be made of the officials of the L.P.D.S.A. and of Mr. & Mrs. C. I. Tighe who gave us all possible assistance throughout our stay in Libya and contributed enormously to the success of the expedition.
Although the Jebel receives a higher rainfall than the remainder of Cyrenaica, much of the water is wasted either by absorption into the underground drainage system or by direct surface runoff, in the latter case causing heavy soil erosion. Locally however the water table rises sufficiently high to enable shallow wells (bir) to be used for a time but the supply is limited and for most of the summer the Bedouin have to rely on springs alone. Perennial springs occur on the coast where they generally discharge straight into the sea, in the beds of a few wadis, and at the outcrops of two marl horizons in the Oligocene and Miocene beds which in the area investigated lie on or above the second escarpment. A large number of springs was visited by the Expedition but it would serve no useful purpose to list them; a comprehensive (though not complete) list of water sources was drawn up during the Italian occupation and is freely accessible. This report will be confined to some general remarks on the existing sources of water, with an account of sources which were thought particularly worthy of improvement and a discussion on the possibility of finding more underground supplies.
The springs visited varied from risings in the lower reaches of wadis with a yield of tens of thousands of gallons per day to small cracks with barely perceptible seepages. In some cases the spring has been piped and led into tanks and cisterns by the Italians, and these installations are of enormous benefit when compared with most of the undeveloped sources, Many of the smaller springs with limited flow (including rock-cut cisterns of classical age) are full of mud, infested with mosquito larvae, and, where animals drink from the spring, leeches are invariably found. In some cases flocks have to be watered by filling stone troughs using old tin cans as scoops.
One spring that possesses most of these undesirable features is Ain Tbelba; O.833595. This source consists of a square rock-cut cistern supplied from a low tunnel. A dry cave alongside was penetrated for some 40 metres without result. The wet cave was explored twice and could be followed by wriggling on one's back in the muddy larva-ridden water with an air gap between the roof and the water of a few inches. This situation appeared to continue almost indefinitely and was not pursued to any conclusion. A short distance up the tunnel however it was seen water flows down a fissure and considerably reduces the yield in the cistern. It is suggested that it would be neither difficult nor expensive to seal this fissure and pipe the water to a tank and trough outside (at a lower level to prevent backing up and possible diversion underground). This spring provides water for settlements up to five kilometres distant, for numerous large flocks and is the nearest supply to Lamluda school. In country where the position of the water table and the relations between springs are matters of delicate balance the alteration of a spring must be approached with caution; one instance of a spring drying up due to the improvement of one nearby was reported to us but there seems little likelihood of such trouble in the case of Ain Tbelba.
During the summer most of the wadis are dry and perennial springs occur only in Wadi Soghi, Wadi Zaigh, Wadi Glaa and Wadi Estua (- upper Wadi Mahboul), in the area covered by the Expedition. Numerous traverses of wadi beds failed to reveal any caves similar to Ain Dubbussia. Small impenetrable caves were associated with a seepage in Wadi Hassan, east of Dubbussia Pumping Station, and a low cave blocked by formations was found amongst thick vegetation in the upper section of Wadi Zaigh. Small springs in the latter and other wadis are too small and inaccessible to be used as a source of supply. The water in Wadi Glaa is piped to a trough, Ain el Halim, in its upper reaches and lower down supplies el Hilal. Ain Estua in Wadi Estua is however capable of yielding a large supply and is no less accessible than Ain Dubbussia and its exploitation would be an operation of similar magnitude. A broken dam and an old gauging dam testify to Italian interest in the spring which has an estimated yield of 100,000 gallons per day. It has been suggested than there exists a Middle Eocene spring forming horizon which is responsible for the water in these wadis. There is no evidence for an impermeable horizon and in some wadis springs occur at several levels. There is a tendency for springs to occur at horizons where thinly bedded limestones overlie more massive beds but in the absence of fossils it is difficult to show that these horizons have any definite stratigraphical position. It may also be noted that with the exception of Ain Estua these perennial springs are all associated vith deposits of Tufa and such deposits may be taken to indicate the probable presence or absence of springs in a wadi.
Two features of interest were noted on the coastal plain. The first, known as Pigeon Hole, is situated beside the road east of Wadi Bu Sahda. This is a circular collapse crater with a mud bottom which is reputed to have been used as a source of construction water by the Italians but would need to be dug out. The second feature is thought to have a similar origin (see Chapter 4) and consists of three depressions known as Abraq Nota. These three depressions lie at the foot of the first escarpment, 14 kilometres west of Appollonia. The largest is the central crater with maximum diameter of some 200 metres. The eastern-most crater is dry but the others contain saline water and were explored by rubber dinghy. Soundings in the central crater gave a depth of 25 metres while the western crater was considerably deeper than this only a few metres distant from its northern edge. These lakes must therefore extend below sea-level and derive their salinity by underground connections with the sea, but, bearing in mind the height of their surfaces and losses by evaporation, there must be a considerable influx of fresh water. A cave leading off the central crater may represent one inlet channel but we were unable to follow this more than a few metres.
The coastal springs also point to the existence of a water table not far below the Sahel. Many of these springs however discharge on the sea cliffs and efforts to develop them have been unsuccessful due largely to the violence of winter storms. It would seem more profitable to attempt to reach the water by well borings, and by using modern divining methods, reasonable success might be assured. None of the potholes explored by the Expedition reached to the water table although several small seepages were encountered. It was quite clear that most potholes had been inactive, that is they have not carried flowing water, for some considerable time. The chief exception is the large pot known as the Garden of Eden. This contains numerous formations including rimstone pools and constant but small flows of fresh clear water. The presence of old jerry cans and oil duums suggests that this water may have been made use of at various times, although the seventy metre climb to the surface would hardly make it a very convenient source. More interesting is the existence of a definite water mark outside the cave which presumably indicates the winter level when the main cave would be full and water would rise into the bottom of the chasm, perhaps 50 metres from the surface. On the whole it seems unlikely that potholes will prove to yield appreciable quantities of water although the possibility cannot be ruled out; Barr Pot (see appendix) contained fair quantities although not readily accessible and in the Lamluda area amongst the many potholes now known, and the many as yet unknown and unexplored, it is possible that a clear way to the water table on one of the spring forming horizons might be found. It is probable that such underground drainage channels that exist are at a considerable depth beneath the surface and have cut downwards due to a general lowering of sea level (Chapter 4) and for this reason are probably most accessible near the present coast.
While supplies for the coastal plain may be found the situation on the high Jebel is less easily dealt with; present supplies are just adequate under prevailing economic and social conditions though they are neither satisfactory nor convenient, Much could be done to improve existing sources, in particular by installing storage tanks and troughs; if water is drawn from a spring during only 12 hours per day, more than half the flow will probably run to waste. Storage of water from winter to summer is hardly an economic proposition under present agricultural conditions and it seems unlikely that even large scale storage, combined with distribution of water from sources such as Ain Dubbussia and Ain Mara, could support irrigation on more than a very local scale.
Perhaps the greatest difficulty encountered in exploring the potholes and caves of Cyrenaica is the initial problem of finding them; although over a hundred occurrences are now known they probably represent only a small fraction of the total. Pothole entrances vary in size from one hundred metres in diameter or may be completely obscured and require excavation as for example Blasted Pot, and it is thus almost essential to employ the services of an arab guide. Due to lack of funds and transport and the necessity of taking account of tribal territories we were not able to retain anyone permanently, however, we were often very fortunate in obtaining local assistance by means of personal introductions and we are particularly grateful to Sheikh Abdullah Assaquri and to Abdussalaam Futuri for their help in this respect.
Even when caves had been found it was not always easy to locate them again on a second visit, prominent landmarks are so scarce that it is impossible to give any detailed directions and map references can only be approximate. In the following section are recorded the principal features of the caves and potholes visited by the Expedition which are not thought to have been explored previously. A number of potholes recorded by the Deep Reconnaissance Unit were also visited for purposes of further exploration, photography and collection of fauna and a list of these is also given. An appendix at the end of the report lists all the caves and potholes explored by the Deep Reconnaissance Unit.
1. El Abiar Pot - 3 km. west of el Abiar. Pitch: 45 m. Pigeons: Not Completed.
2. Blasted Pot - O.886565. Pitch: 10 m. Narrow opening covered by boulders, dug out and later covered over. Foul Air, no continuation.
3. Brownsquaredone Pot - P.084594. Pitch: 5 m. No continuation.
4. Covered Pot - P.892564. Pitches: 3 m. 5 m. Entrance in roof of first chamber. Second small chamber at base of second pitch with possible dig and a tight squeeze.
5. Crack Pot - O.842580. Pitch: 18 m. Awkward Belay, small seepage at bottom. No continuation.
6. Dead Dog Pot - O.880565. Pitch: 13 m. Climbable, mud choke. No continuation.
7. Elizabeth Pot see Nick Pot
8. Fuss Pot - O.867555. Pitch: 10 m. Climbable, mud choke. No continuation.
9. Haua bu Nagela - O.809585. Pitches: 24 m, 10 m. Entrance on east side of Wadi, first pitch leads to vast chamber. Climb over large boulder pile with bizarre sculptured rock formations leads to passage with roof scallops on large scale. Beyond a chamber inhabited by thousands of bats, floor a thick pile of dung. Low opening on left leads to short passage and second pitch. Artificial belay needed. Possible dig, otherwise no continuation. Photographed. Fauna collected.
10. Nick Pot - O.833576. Pitches: 10 m. 40 km. Oval collapse-type depression c. 40 m. diameter with thick undergrowth. First terrace 30 ft, below surface has small cave becoming a low crawl for 25 m. Climb aven to small cave at bottom of Elizabeth Pot. Pitch 3 m. Main (Nick) Pot:- 10 m. pitch climbable from first terrace leads to second terrace and small cave with possible tight squeeze. Belay to large boulders for second pitch but air foul. Second pitch not completed. Formations.
11. Nollo Pot - 4 km. north west of Safsaf. Pitch: 15 m. Pitch ends on boulder pile, large chamber. Pigeons and human skeleton. Low passage with formations. No continuation.
12. School Pot - O.861556. Large collapse crater. Low cave might be dug with much labour. Local reports of subterranean rumblings during wet season.
13. Shai Pot - O.852563. Pitch: 50 m. No belays. Not attempted.
14. Shell Pot - O.895566. Pitches: 6 m, 22 m. First pitch climbable. Formations, bats. No continuation.
15. Tea Pot - O.838577. Pitch: 13 m. Enlarged clints in T shape. Pitch ends on boulder pile in chamber. Attempt to dig further foiled by lack of air.
16. Osegi Pot - P.030454. Pitch: 8 ~n. Pitch climbable leads to two passages, both without continuation.
17. Abraq Nota - O.563674. 14 km. west of Susa, Cave in south west corner of eastern saline lake. Follows N-S Fault line. Reached by dinghy and climbing over 10 m. boulder pile due to cliff fall. Further cliff falls taking place continuously. Cave explored by dinghy but after 10 m. roof meets water. Probably a fresh water inlet.
18. Ain Kamise - P.008050. Small cave 4 m. with spring.
19. Ain Tbelba - O.833595.; See also chapter 3. Dry cave: 40 m. ends in narrow fissure; low crawl. Wet cave: can be negotiated by crawling on back in water with small air gap. Not completed. 40 m. +
20. Ain Umm Ammesc - O.818577. Low opening beside small spring. 12 m. low crawl to shallow pool where 7 m. low mud floored passage without continuation.
21. Hassan Cave - P.030616. Low passage near wadi bed. Tight squeeze not overcome by digging or chipping.
22. Garden of Eden - O.743555. Large oval crater 100 m. in diameter. 70 m. climb down through cacti and boulders leads to cave entrance. Enormous chamber with sloping mud floor leads down a further 38 m. Formations, some water, See Chapter 3.
23. Pigeon Cavern - O.825489. Pitch: 16 m. Pigeons.
24. Pigeon Hole - O.862698. Collapse crater on south side of coast road. 10 m. deep.
25. Swallet Hole - O.849554. Pitches: 35 m. 10 m. lacks fresh air.
26. Ain Dubbussia - Bats. Photographed.
27. Lethe - Benina nr. Benghazi. Surveyed, Photographed, fauna collected.
28. Susa Cave - correct name not known. On west side of wadi 5 km. west of Susa, well known to local population. A succession of chambers with very fine formations, walls often covered with inscriptions.
29. Trouser Cave - correct name and exact position not known as in rough country near Wadi Hassan. Used as retreat by Senussi during war with Italians.
The approximate positions of most of these caves are shown on Map 1.
The caves visited by the expedition were usually in wadi beds and either were or had been associated with springs. Few could be penetrated for any great distance and from the spelaeologists' point of view are generally rather uninteresting. Ain Dubbussia was visited on two occasions and its several passages explored and photographed. There is no possibility of further exploration except by the hazardous process of diving. There are however some interesting mud formations carved out by water dripping from the roof.
Much more spectacular formations of dripstone were found in the Susa Cave. This cave is situated high on the west side of a wadi with only a small entrance under a large overhang of rock. This outer "porch" to the cave is largely formed of dripstone indicating that the wadi has been cut back into the cave and that the present opening is not the original one. There are several large chambers whose walls carry many inscriptions and graffiti in Greek script. Although avens and passages were thoroughly explored and a small dig attempted no continuation was found.
Potholes are also somewhat disappointing spelaeologically, the most common type consists of a vertical shaft ending on a conical pile of mud, boulders and pigeon droppings, and, beyond a chamber or short passage, there is no continuation possible except by energetic digging. It was not thought worth while undertaking digs as regards finding water was concerned and in several cases such work would have been hampered by foul air. It was unusual to find more than one pitch needing ladders, however depth proved to be no criterion of difficulty, one of the hardest pitches was the 10-metre pitch of Blasted Pot which even after excavation needed a tight squeeze at the top which entirely defeated one member of the party. Haua bu Nagela was probably the most interesting pot visited, not only on account of the large bat population that was thrown into confusion by our entrance with ladders and flashguns; the underground section was more extensive than usual and the roof and walls showed large flow scallops; rooks on the large boulder pile were also water-worn. No continuation beyond the second pitch was possible without digging.
The accumulation of debris in all the potholes visited indicates that active development ceased some time ago and, with the exception of Ain Dubbussia, the same might be said of the caves. It is in any case clear that neither wadis nor cave systems could form under present climatic conditions, indeed many potholes with shafts showing solution features are now unable to receive any drainage since their entrances lie on top of small rises, e.g. Tea Pot. This latter pot is also an example of a pothole developing by enlargement of clints but several other definite solution shafts were seen. The more spectacular Cyrenaican potholes or "Haua" are those which appear to have formed by collapse e.g. Black Well north of Labraq which is at least 50 metres in diameter at the surface and 200 metres deep (See appendix). The best examples of collapse features are Pigeon Hole and the saline lakes of Abraq Nota on the coastal plain. These depressions can only have arisen by subsidence since a clean cut hole has been punched through both bedrock and alluvial deposits. Since the latter have not filled the depressions subsidence must have occurred at comparatively recent date. Soundings taken in the Abraq Nota lakes indicate that their floor lies below present sea level and there is some underground connection with the sea, the level being maintained by continuous inflow of fresh water. (See Chap. 3)
One side of the central depression coincides with the line of a small N-S fault but in other cases the depressions are roughly circular and in no way determined by faulting. It is probable then that collapse craters were formed by the subsidence of the roofs of caverns developed when the sea level was lower than at present. There is abundant evidence of such a retreat of the sea during the Pleistocene, perhaps to a level of -90 m. during the last glaciation when it is probable that climatic conditions were favourable to cavern development in Cyrenaica (Chap. 6). The evidence from these lakes suggests a retreat of the sea at least of the order of 25 m.
The collapse craters of the high Jebel also appear to have formed by subsidence of shaft walls and cavern roofs. The first stage of pothole growth was the development of solution shafts followed by cave enlargement underground. Nick Pot (See Map 1) probably represents an intermediate stage at which collapse is beginning to occur. Finally a large crater is produced which eventually fills with debris.
It can be seen from Map 1 that most of the known potholes are situated above the upper escarpment; this may be a true picture of the distribution but it should be remembered that the ground below and to the north of the second escarpment is severely dissected by wadis and less accessible, making exploration more difficult. The upper escarpment is thought to be an ancient shoreline (Hey 1956) and one might therefore expect the ground above it which has been exposed to erosion for a longer period to have developed more karst features and it is possible that some of the potholes and cave systems began to develop during the Pliocene Period. Successive regression of the sea and the intermittent wet periods of the Pleistocene would have caused a gradual lowering of the water table and cutting down of passages. The present stage of the potholes is probably due to lack of rainfall in recent times arresting further development and allowing accumulation of fallen debris.
Hey R.W. 1956. The Geomorphology and Tectonics of the Gebel Akhdar (Cyrenaica). Geol. Mag. XCIII pp. 1-14.
The Expedition was loaned a certain amount of collecting equipment by the British Museum (Natural History) in order to make a collection of cavernicolous animals (it was felt unwise to embark upon a more extensive field of collection with the limited means available).
Deep caves provide a very specialised environment with constant temperature and humidity, a complete absence of light and usually a very limited food supply. A number of animals have adapted themselves to this very particular habitat and it is those inhabiting the dark-zone rather than the intermediate twilight that are of greatest interest in this respect. Unfortunately we found few caves with an extensive dark-zone, and most of these were dry and yielded very few specimens.
We have presented to the British Museum the following specimens:-
The prawn Typhlocaris lethaea was the main reason for our visit to a cave at Lethe near Benghazi which the ancient Greeks had thought to be an entrance to the underworld. This species of prawn occurs only in this cave, and has not often been collected.
Of the bats, Rhinolophus mehelyi is not commonly collected but has been recorded from Egypt and Algeria. Miniopterus schreibersi is widespread in the Mediterranean region, and has been found in Algeria but not as far east as Cyrenaica. We saw bats in four caves but could only catch them in one, Haua bu Nagela, where there was a well established colony of both species - Miniopterus greatly predominating. The heap of dung beneath them was visibly fifteen feet high, and there was a considerable unmeasured depth beneath the point of observation.
Unfortunately at the time of writing one box of specimens and equipment has not yet arrived from Benghazi, having been detained by the Customs Authorities.
This box contains bat ectoparasites, some Coleoptera and other animals from the bat dung; various Diptera from within caves, a number of other specimens that await identification, and notes on the behaviour of Typhiocaris lethaea.
We are most grateful to the staff of the British Museum (Natural History) for assistance in preparing for the expedition, the loan of equipment and the identification of the specimens.
The village of el Atrun is situated at the foot of the first escarpment some 35 km. west of Derna and about 12 km. to the east-south-east of Ras el Hilal. At this point the coastal plain is less than 1 km. wide and is composed partly of normal alluvial and scree deposits and partly of tufaceous deposits derived from the wadi system which reaches the sea at this point. The main wadis in this system are Wadi es Seghi and Wadi Zaigh, the former stretching for some 8 km. to the south and cutting back into the second escarpment. These wadis are unusual in containing a number of perennial springs many of which have a considerable yield, which, by a system of aqueducts, enables quite extensive irrigation and cultivation to be carried on at el Atrun. The tufaceous deposits of the coastal area were described by Hey (1955) who considered them to be contemporary with the first stages of the Würm Glaciation. The proximity of the Expedition's Base Camp to el Atrun enabled a study to be made over a wider area and to show that deposits of several ages and types are present. Wadi es Seghi was surveyed by means of an abney level and prismatic compass traverse, supplementary points being obtained by pacing and use of aneroid barometers; Wadi Zaigh was less accurately mapped due to its greater inaccessibility but numerous aneroid levels were taken on several occasions and the survey was completed from a special subsidiary camp near el Atrun. As regards the coastal tufaceous deposits we have little to add to the description given by Hey but it will be convenient at this stage to give a brief account of this area before dealing with the deposits in the wadis. Throughout the following account these tufaceous deposits will be referred to as the el Atrun Deposits.
The el Atrun Deposits are exposed in the vertical cliffs and inlets of the coast and in the sides of the wadi which follows a winding course from the confluence of Wadi es Seghi and Wadi Zaigh just south of el Atrun to the sea. For much of its length this wadi, sometimes known as Wadi el Atrun, is very narrow and deep, the present watercourse being in places only two metres wide with nearly vertical sides of soft Cretaceous limestone with horizontal bedding disturbed in places by small east-west faults and minor slump structures. The el Atrun Deposits rest on a rather irregular limestone surface which can be seen in places to be crossed by channels usually filled with a pebbly facies of the Deposits. In the cliff sections the Deposits are seen to be composed almost entirely of red tufa with impressions of leaves and stems of plants, completely covering a limestone cliff and extending below present sea level. Further inland there are varying proportions of tufa and pebbles of limestone so that often the deposits are more deserving of the term gravels. The alluvial deposits of adjoining wadi mouths, the "Younger Gravels" of McBurney & Hey (1955), are quite distinct however in their total lack of tufaceous material. Hey interpreted the exposures at el Atrun as follows:- The tufa was formed largely on the cliffs at a time when the sea level was lower than at present, the supply of water somewhat greater and the stream changed its course across the sahel as its outfall became blocked by the accumulation of tufa. As the deposits rest upon a 3-metre shelf which is elsewhere associated with the 6-metre shoreline the deposits are taken to be later than that feature, while the flora and fauna suggest an age greater than that of the "Younger Gravels". Finally a diminution of the supply of water led to the cutting of the present gorge across the sahel.
In the following account of the inland area it will be found helpful to refer to the map at the end of the report.
The el Atrun deposits are easily traced into Wadi es Seghi where gravels occur on both sides of the wadi usually surmounted by a definite terrace. A short distance above Ain Balbo this terrace occupies a large meander which has been cut off at a later date. Upstream of this area there is no continuous exposure of these beds but two occurrences of tufaceous gravels which on account of level and lithology may be correlated with the el Atrun Deposits, are found north of Ain Lug. The wadi sides in between are masked by vegetation and scree deposits. These two patches of gravels are however banked against deposits of homogeneous red tufa of clearly earlier date. This tufa extends above Ain Lug and up Wadi es Seghi towards Ain Sidi Mahmud. The upper surface of this tufa is a well defined terrace 6 metres higher than the el Atrun Deposits terrace. This mass of tufa, which will be referred to as the Sidi Mahmud Tufa, appears in turn to be younger than another extensive spread of tufa which is found on the sides of the wadi above it and which extends up the wadi to a short distance below Ain Dubbussia and will be referred to as Dubbussia Tufa. In places Dubbussia Tufa is capped by a definite terrace or platform but in general the Dubbussia tufa is more heavily weathered than Sidi Mahmud tufa, frequently partly obscured by scree and deeply eroded by the stream. Near Ain Calipha however an obvious terrace exists and is flanked by a lower terrace which continues for some distance down the wadi below the junction with Wadi Haddadir.
The tufa underlying this lower terrace is lithologically indistinguishable from the Dubbussia tufa; it seems however to be younger than Dubbussia tufa and, in the absence of any further deposits of tufa in this part of the wadi, is probably contemporaneous with Sidi Mahmud tufa, although it should be emphasised that there is no direct connection between the two outcrops.
In the upper part of the wadi a coarse breccia is found below the Dubbussia tufa consisting of angular blocks and fragments of limestone with a calcareous cement. This deposit is very similar to the cemented scree deposits occurring on the wadi sides but its exact mode of origin is doubtful. The succession worked out in Wadi es Seghi is therefore as follows:-
El Atrun Deposits Sidi Mahmud Tufa ) probably equivalent in age. Calipha Tufa ) Dubbussia Tufa Breccia
The section of Wadi es Seghi above Ain Dubbussia was traversed but does not contain any waterlaid deposits and is therefore omitted from the map.
The features described above have been interpreted as evidence for three main phases of deposition of tufaceous deposits, each of which was followed by a period of erosion. Deposition of tufa is a process of aggradation and each individual deposit is surmounted by a terrace. The question arises therefore as to whether these terraces might be purely erosional and the deposits all more or less comtemporaneous. The various deposits of tufa are indeed lithologically very similar, being red in colour, massive, and frequently containing intercalations of pebbles, furthermore the deposits inland do not seem to contain an either abundant or distinctive flora. Since successive deposits of tufa are "welded" or cemented on to the underlying beds stratigraphical breaks are rendered less obvious. However in one of the waterfalls below Ain Calipha a probable unconformity was seen between Calipha Tufa and Dubbussia Tufa. In support of the existence of three phases of deposition one may cite the fact that El Atrun gravels are banked against Sidi Mahmud Tufa, that Dubbussia Tufa is the most heavily weathered of the deposits and that just below the junction of Wadi es Seghi and Wadi Haddadir Calipha Tufa can be seen to have formed on a small waterfall in limestone, the surface of the terrace also reflecting this drop, whereas there is no evidence of this feature in Dubbussia Tufa opposite. Erosion terraces indeed were mapped in the wadi, particularly in the el Atrun Deposits.
Mention should also be made of the occurrence of more recent deposits of tufa than those described above. Small isolated patches were found adhering to the walls of Wadi el Atrun and a more extensive deposit was found on the face of a small waterfall a short distance below Ain Sidi Malimud, where a very striking unconformity on Sidi Mahmud Tufa is exposed. These deposits have all been mapped as "Recent Tufa" although there is no evidence of contemporary formation. Some of this tufa in Wadi el Atrun still contained reed stems although the deposit as a whole, which must have been several metres thick, has been almost completely removed by erosion.
Whereas the el Atrun Deposits are continuously traceable into Wadi es Seghi, correlations with the deposits in Wadi Zaigh are somewhat less certain. In the lower part of Wadi Zaigh there are several outlying patches of red gravels with terraces lying at considerable heights above the present wadi bed, which follows a very winding course. Beyond this lower gorge the wadi opens out and the wadi bed occupies an almost vertical sided narrow trench some 30 metres deep cut into a definite terrace underlain by deposits of gravels similar to those at el Atrun. Levels were taken along this terrace and on the isolated terrace fragments "downstream" and the conclusion reached that these deposits were equivalent to the el Atrun Deposits. This terrace continues into Wadi el Gazul and extends up Wadi Zaigh as far as a prominent cliff of tufa 20 metres high.
At several localities in Wadi Zaigh a higher terrace is present which can sometimes been seen to be underlain by gravels of a different type, these occurrences have been mapped as "Higher Gravels" and are thought to represent an earlier phase of deposition. From the scattered nature of the outcrops these gravels must have occupied the greater part of the wadi up to the tufa cliff although the wadi may not have been as wide as it is at present. These gravels are not tufaceous and lack the red colour of the other deposits, although this might be due to later weathering.
The cliff of tufa referred to above rises above a small arab settlement centred round a group of palm trees and this tufa has therefore been called Palms Tufa. The tufa cliff does not appear to be an original depositional feature as outlying masses of tufa are found lower down the wadi. Fallen blocks of tufa are found on the el Atrun Deposits terrace while a terrace which caps the tufa is higher than the Higher Gravels Terrace, which is therefore interpreted as a younger feature,
Flanking the Palms Tufa and lying above its terrace on the sides of the wadi are outcrops of older more weathered tufa. This, mapped as Higher Tufa, is only a fragmentary deposit but represents a further stage of tufa formation.
The wadi beyond this outcrop was explored and found to contain occasional outcrops of tufa and a few small springs, however the steepness of the wadi sides, combined with the denseness of the vegetation, made progress difficult and mapping impossible. The sequence determined in Wadi Zaigh is as follows:-
El Atrun Deposits Higher Gravels Palms Tufa Higher Tufa
As in Wadi es Seghi, erosion terraces were mapped in the el Atrun Deposits.
Before proceeding to a discussion of correlations an account is here given of present day formation of tufa in Wadi es Seghi. Due to diversions into aqueducts water does not flow throughout the length of the wadi from Ain Dubbussia, however over much of the present watercourse tufa is being deposited. In recent times water had not issued from Ain Dubbussia until the exploitation of this spring as a water supply, and at the time of the expedition's visit water had only been flowing for two years. Tufa is not being deposited in the stream bed until the ford below the spring is reached, which is also the point at which Dubbussia Tufa is first met. The rate of deposition estimated on the face of one of the waterfalls below this point is of the order of 15 cm. thickness per year. This modern tufa does not possess the red colour characteristic of the older deposits. Tufa appears to form most readily on waterfalls and rapids and attached to mosses growing in the water. Factors which probably contribute most to its formation are some degree of splashing or spray causing evaporation and aeration, and a rise in temperature, while biochemical reactions caused by plants, e.g. mosses, may be a further possibility. (c.f. McBurney & Hey, 1955 p. 116 et seq.) Several examples of tufa forming on waterfall faces can be seen amongst the older deposits and some of these "tufa falls" have been mapped. In some cases the original rock step can be seen, in others the presence of steeply dipping "bedding planes" is the only evidence. Under conditions of tufa formation there is therefore a tendency for the bed to be raised in level rather than be eroded and for the faces of waterfalls to advance rather than recede. A further point of interest is the occurrence in Wadi es Seghi of "rimstone pools" exactly similar to those found in caves, i.e. round pools edged with tufa which is continually being added to.
One of the interesting and puzzling results of this survey was the differences between the successions in Wadi es Seghi and Wadi Zaigh which one might have expected to have a similar geological history. The basis for correlating between the two wadis is the presumed presence in both of the el Atrun Deposits and although some doubt inevitably attaches to linking up of deposits and terraces across gaps, we feel that the correlation of the el Atrun Deposits worked out in the field is the most probable one.
If this correlation is accepted then the next problem is that of the status of the Higher Gravels of Wadi Zaigh. It might be tempting to correlate the two phases of tufa deposition that occur in both wadis before the el Atrun Deposits, however since it appears that the Higher Gravels formerly occupied a much larger area presumably they also represent a major period of aggradation followed by a period of erosion. Therefore a direct correlation between the wadis is proposed:-
WADI ES SEGHI WADI ZAIGH WADI EL ATRUN Recent Tufa Recent Tufa Erosion Terraces Erosion Terraces Erosion Terraces El Atrun Deposits El Atrun Deposits El Atrun Deposits Calipha-Sidi Mahmud Tufa Higher Gravels Dubbussia Palms Tufa Breccia Higher Tufa
It is clear that the tufaceous deposits under consideration must have been formed at a time when the rainfall was much higher than at present and the volume of water issuing from underground sources correspondingly far greater. The occurrence of gravels at an earlier date in Wadi Zaigh however may be due to a greater proportion of the flow in this wadi having been derived from surface runoff, a smaller proportion having come from springs. Intercalcations of pebbles are common in the Sidi Mahmud-Calipha Tufa but clearly springs were very active. Of the two wadis, Wadi Zaigh has the larger catchment area at present and a very few small springs, while the springs of Wadi es Seghi produce a large and constant flow.
It seems most likely that the erosion of deposits took place under conditions of comparatively reduced rainfall, smaller streams cutting deep narrow and winding trenches through the tufa and gravels. There is little doubt that at some time springs existed in Wadi es Seghi at a higher level than Ain Dubbussia and if they were associated with deposits of tufa then these also have been removed. Although no genetic implication was intended by naming deposits after springs, springs in fact were the only known named features in the wadis, it is clear that springs were active at progressively lower levels as time went on and that, for example, the resurgences of Ain Calipha and Ain Sidi Mahmud were probably responsible Łor the development of Calipha and Sidi Mahmud Tufa since the top surfaces of these deposits extend towards the level of the springs. These relationships will be most clearly seen on the section on Map 2.
In the absence of fossil evidence it is clearly unwise to attempt to establish a rigid correlation of the deposits of such a small area. It is also unfortunate that the succession of shorelines recognised on the first escarpment (McBurney & Hey 1955) is not well represented in the el Atrun Area and the only reasonable dating is that of the el Atrun Deposits as later than the 6 m. shoreline which was proposed by Hey (1955). The "Younger Gravels" Erosion Terraces and "Recent Tufa" are features younger than the el Atrun Deposits and show apparent evidence of a changing climate in geologically very recent times. In view of the complexity of the tufaceous deposits of this area, the lack of reliable criteria of age and the dangers of making too many assumptions regarding climatic conditions we have not attempted to establish any further correlation.
McBurney C.B.M. and Hey R.W. 1955. Prehistory and Pleistocene Geology in Cyrenaican Libya. Cambridge.
pp 21-46 of the report (Chapter 7 - Social Studies) are not reproduced.
The existence and success of the Expedition was in very great measure due to the extremely generous support that it received both materially and in personal assistance. We therefore wish to record our most grateful thanks to the following organisations and individuals.
Finally we wish to thank Miss J. Holland for her valuable assistance in producing this report.
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