The physiography of the river Nile and is basin . > and the Atbara. / This trough was determined in the first instance by - fractures of the crust which caused a strip of country from about Edfu(hit. 25° N.) to Cairo to be depressed, leaving the plateau standing highabove it, just as the Ked Scii and the gulfs of Suez and Akaba wereformed, probal)ly about the same epoch. This intiirference with thedrainage of the country doubtless produced a series of lakes in the low-lying area, Avhile the drainage of the eastern jjlateau conunenced toexcavate the valleys wliich now exist as dry desert wad
The physiography of the river Nile and is basin . > and the Atbara. / This trough was determined in the first instance by - fractures of the crust which caused a strip of country from about Edfu(hit. 25° N.) to Cairo to be depressed, leaving the plateau standing highabove it, just as the Ked Scii and the gulfs of Suez and Akaba wereformed, probal)ly about the same epoch. This intiirference with thedrainage of the country doubtless produced a series of lakes in the low-lying area, Avhile the drainage of the eastern jjlateau conunenced toexcavate the valleys wliich now exist as dry desert wadies, their develop-ment being in many cases far from complete as shown I)y the cliffs whichinterrupt the .slope of the valley wlien a hanU^i- bud of rock than usualis met with. Into this depressed area the drainage of the southci-n |)ai-t of thebasin finally floAved, and there laid down the alluvial deposit through » r. S. Geol. Survey, 19th Annual report Part If, Washington, 18!I9, p. 93. i THE BASIN OF THE NILE. ASWAN - CAIRO. PLATE Scale Km. so 40 so to 10 0 L-J I L_l 1 MHt> so 40 80 30 10 0I l___J , l_ ISO 100 Km. OftlAQ - MAWeA ,3Jm; 3HT 10 KIK • 0« M «• t .1 -« — ) — which the rivci-flows to-day : so rli;it unilcr tlic present conditions thesolid geology of this part has but little effet-t on the physical conditionsof the river. Tlie almost horizontally bedded strata of sandstone andclay in the southern area and of limestone in the northern part dip verygently in a northerly direction but it is only at a few points that theriver washes them; for the most part it is confined within the limits ofthe alluvial plain. Every few years slight eartlupiake tremors show that movement alongthe lines of facture has not whollv ceasL(l and tliouuh tliese of recentyears March 28, 184fi, October 12, 1856 and June 24,1870 for instance,have been on the whole slight, in 1808 a very violent shock occurred onAugust 8 by which m\ich diiiiiage and serious loss of l
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