With the withdrawal of the Roman garrisons and the Mohammedan conquest decay set in, and, as Sayce remarks, the aqueducts became choked, the fields were neglected, and malarial fever invaded a district which had at one time been regarded as a health resort.
Of the history of the oases during the succeeding seven or eight centuries no records are available, but, judging from the writings of Arabian geographers, between the eleventh and the fifteenth centuries, it is evident that they gradually became depopulated, and were regarded as of little importance. El Sherîf el Edrissi, writing about the middle of the sixth century of the Hegîra, refers to the oases (Al Vahat) as places formerly containing streams of water, with lands on which trees were still found growing, and with ruined, uninhabited towns. He adds that the goats and sheep had become quite wild, and were trapped by hunters like other wild animals. It is not improbable, however, that this author was referring to some of the smaller oases-depressions, such as Kurkur, or perhaps to some of the more outlying parts of Kharga or Dakhla. It seems extremely unlikely, as Hoskins remarks, that the Great Oasis as a whole had become entirely uninhabited.
Still later the emir and historian Ismail Abulfida, about the beginning of the fourteenth century, speaks of the oases as abounding with palms and running water, and describes them as situated like islands, in the middle of the desert, three days’ journey from the Said (Upper Egypt). Jacutus describes the positions of three oases, and refers to the first of them as being well cultivated, containing streams and hot springs, palms and cultivated lands. The inhabitants, he adds, are in a wretched state. Several other writers allude to the Egyptian oases, but their information is seldom, if ever, first hand, and the descriptions are in general so vague that we are left in doubt as to which particular oasis their remarks refer.
The more modern records, commencing with those of Poncet at the end of the seventeenth century, have already been referred to in a previous chapter.
CHAPTER VIII
THE EXTINCT LAKES OF THE OASIS
Character and Extension of Lacustrine Deposits — Modern Erosion by Wind-borne Sand — The Lakes geologically of Recent Age — Discovery of Pottery and Bones of Domesticated Animals — Area occupied by the Lakes — Maximum Level of their Waters — Lacustrine Strata at Gorn el Gennâh — Relation to the Ancient Monuments — Altitudes of Archæological Sites — Age of the Lakes and their Persistence into Historic Times — Flint Implements — Origin of the Lakes — Their possible connection with the Artesian Waters — Lacustrine Deposits form the Cultivated Lands of Modern Times.
When in 1906 I commenced to make a special study of the geology of the oasis, with a view to elucidating certain questions which had arisen in connection with the water-supply, it came to me as a very great surprise to find indubitable evidence that the greater part of the floor of the depression had at one time or another been the site of an immense lake. No mention had been made by previous observers of the extensive accumulations of lacustrine sediments which cover so large a proportion of the floor, and are found from near Ain el Ghazâl in the north to beyond Beris in the south.
LACUSTRINE DEPOSITS AT EL GALA, NEAR BULAQ.
These deposits consist of horizontal finely-bedded alternations of sand and clay, or more frequently of an intimate mixture of the two; local false-bedding is not uncommon, and included fragments of limestone or sandstone are occasionally met with. The beds have a prevailing brown tint, and frequently exhibit well-marked hexagonally disposed shrinkage cracks. Although originally they must have formed an immense compact and continuous sheet, the deposits have since been subjected to considerable denudation, so that at the present day they exist as large isolated patches. Perhaps the most striking of these is that occupying the centre of the depression between Kharga village and Jebel el Ghennîma, covering an area of between 40 and 50 square kilometres, and over the greater part cut by the sand-blast into thousands of isolated hummocks, disposed with their longer axes parallel and in the direction of the prevailing north winds. Individual hummocks have perhaps an average height of 4 or 5 metres, though many exceed this considerably; in length they may measure anything up to 40 or 50 metres. The northern end of a hummock is in nearly all cases the larger, the gradual tapering towards the south being a most distinctive feature. Their present shape and appearance are, of course, entirely due to the eroding and sculpturing action of sand-laden wind.