Some Recent Geological Deposits in the Egyptian Nile Valley

Abstract

Several years ago G. W. Murray I contributed a discussion to the Geographical Journal which m rked the first successful attempt o sketch the Upper Pleistocen and Holocene climatic history of Egypt in a truly modern fashion. The wealth of personal observations and intimate knowledge of the material described reflected Mr. Murray's long years of experience in Egypt, since 1941 as Director of the Topographi? cal Survey. During the winter of 1958 the present writer collected geological data in Middle and Upper Egypt which adds in some way to our present knowledge of Postglacial climates in that country. Although the Recent, or Holocene, deposits of Egypt form but a minute fraction of the surface area, their significance for the inhabited riverain zone is paramount. Climate and sedimentation must have played as important a role in modelling the geographical environment in ancient times as they do today. For example, it is not at all obvious that the precious Nile alluvium has been distributed and laid down at a uniform rate since the close of the Pleistocene, as is widely supposed. These Holocene deposits in the Nile Valley are of aeolian and fluviatile origin: sand dunes, nilotic mud and wadi deposits. The aeolian deposits.?Wind-borne sediments in the valley are more or less limited to the western margins, particularly between Gebel Deshasha (near Biba) and the monas? tery Deir el-Miharraq by el Qusiya, a stretch of over 80 miles. These sand fields are of considerable hindrance to cultivation. Their development is both complex and interesting, so that it is regrettable that, apart from reference to their existence, little attention has ever been paid to them. Firstly one can speak of an irregular line of marginal valley dunes lying exlusively upon Nile mud to a width of one half to two miles between Deshasha and a point about three miles south of Balansura (west of Abu Qurqas). After a small interruption similar dune fields occur between Tuna el Gebel (west of Mallawi) and Dashlut (west of Dairut), and again between Nazlet Bawit (west of Sanabu) and el-Miharraq. In contrast to the dunes upon the Pleistocene gravels west of the desert margin, these are to a fair extent fixed by vegetation deriving its moisture from the ground-water. Although the fields between Deshasha and Bal? ansura can only be classified with difficulty as generally transversal arrays running paral? lel to the border desert-alluvium, those between Tuna and Dashlut are developed as specific geomorphological forms. Three rows of 10 feet high transversal dunes run NNE.-SSW. while another line abuts the desert in the lee of the Pleistocene gravels. In the Meir area, between Sanabu and Qusiya, two immense longitudinal dunes of four miles in length are blown up in the lee of the steep limestone scarp running NNW.-SSE. All these dunes overlie nilotic sediments and were apparently deposited during the last few centuries. From behind the Black Hills due west of Beni Mazar a chain of NNW.-SSE. longitudinal dunes, generally averaging one or two miles in length, extends over 30 miles across the desert surface to the nummulitic headland a little south of Balansura.