PREFACE.
This book is an attempt to give a systematic account of the geography and geology of South-Eastern Egypt according to the latest information available. It is based on surveys which I carried out by order of the Egyptian Government during the four years 1905-1908, and has been written in the intervals of other official work during the succeeding three years.
In the first or introductory chapter, I have given a summary, with some criticisms, of previous accounts of the region. This seemed advisable in that the literature, although not very extensive, is scattered in books and papers in various languages, and is not always easy of access.
The second chapter is a concise systematic account of the district, designed mainly as a summary for those who do not wish to go into the details; it also contains sections dealing with matters of insufficient importance, or of which our knowledge is too scanty, to be treated of specially in the succeeding chapters.
The third chapter is an account of the surveying methods employed and the principal geographical results obtained. The surveying methods are treated at some length, firstly because an adequate specification of the survey methods used is necessary for the assessment of the value of any contribution to modern geography, and, secondly, because some of the methods are either new or little known, and have been found by experience to be specially adapted to the mapping of this type of country. The principal geographical results are given, mostly in tabular form, as exhibiting clearly the groundwork of the actual maps, and as indicating a series of adequately fixed positions which may be employed as a basis in any further surveys.
In the fourth to sixth chapters the drainage lines and hill features are systematically described. A knowledge of the drainage lines, as the key to a precise understanding of the relief, is nowhere more important than in these deserts.
In the seventh chapter the important question of water supplies is considered, and the positions and particulars of the various water sources are tabulated for easy reference.
The eighth to tenth chapters deal with the various rocks occurring in the district. The petrology of the region has been discussed with some fulness, because while the district offers a remarkable wealth of rock-species, well exposed in considerable masses, detailed studies of Egyptian petrology have hitherto been few. My great regret in this connexion is that I have been unable to add chemical analyses of the rocks.
The eleventh chapter summarises the general geological structure and history of the region, as gathered from a broader outlook over the detailed geological evidences.
In the twelfth chapter I have set down the information I was able to obtain regarding the territorial limits of the different Bedouin tribes inhabiting the region.
The thirteenth and concluding chapter of the book consists of brief notes taken on the return march to Port Sudan.
In regard to the cartographic material, most of which is new, special attention has been given to the place-names, and it is believed that these are correct in almost every case. But as the names are in languages not understood by European draughtsmen, it is almost impossible that mistakes have been entirely avoided; in any case where map and text may disagree in spelling (the differences will, I trust, never be so great as to leave doubts of identity), the text should be followed in preference to the map, as mistakes in the text are usually more easily perceived and corrected. I would remark that although the whole of the field maps have been employed in preparing the small scale ones, yet the full detail can be recorded only on the large scale maps, which are given for the most important districts; a future explorer would do well, therefore, to refer to the manuscript field maps which are filed at the Survey Office at Gîza, before concluding that no more detailed survey exists than is shown on the maps in this book.
The plates illustrating the scenic types are from my own photographs, while those illustrating the natural-size aspect of the typical rocks are reproductions from water-colour drawings which I made from actual specimens. These coloured plates of rocks are mainly designed to enable prospectors to identify readily the ordinary kinds of stone they meet with in the field; but they will also serve to give to petrologists an idea of the appearance of hand specimens of rocks from this part of the world, which are not frequently met with in the great museums. The text figures of rock sections I have mostly drawn at the microscope on silver prints from photographic plates, the prints being afterwards bleached out with mercuric chloride; they will appear slightly diagrammatic in places, owing to the necessity of using lines and dots for tints, but I find I myself get a better idea of a rock from a drawing of this kind than from a photograph.
Much detailed surveying of this mountainous and arid region remains yet to be done, especially in the districts round the heads of the Wadi Alaqi, before our knowledge of it can be considered complete. It is hoped, however, that a substantial beginning has been made towards this end, and that future work may be facilitated by the observational data recorded in the following pages.
John Ball.