234 



out a tolerable uniformity of character, we may be justified in 

 holding the portion that has taken place within the historical period 

 to afford a measure of the time occupied in the production of the 

 antecedent part of the same change. 



Egypt supplies us with the earliest evidence of the existence of 

 the human race recorded in works of art ; in its monuments we find 

 the dawn of the historical period and of civilization ; and that land 

 alone, of all parts of the world as yet known to us, offers an instance 

 of a great geological change that has been in progress throughout 

 the whole of the historical period, in its annual inundations and the 

 sediment these deposit to form the alluvial land in the valley of the 

 Nile ; and there is good reason for believing that the change had 

 been going on with the same uniformity for ages prior to that period 

 when our reckoning of historical time begins. To investigate the 

 formation of the alluvial land in the valley of the Nile in Upper and 

 Lower Egypt is therefore an object of the highest interest to the 

 geologist and the historian. 



The author being impressed with the conviction that this geolo- 

 gical problem could only be solved by having shafts and borings 

 made in the alluvial soil to the greatest practicable depths, deter- 

 mined to have some such experiments made ; as the results might 

 lead the way to other researches on a greater scale. The ground on 

 which he hoped to be able to form a chronometric scale by which 

 the total depth of sediment reached might be measured, was the 

 same as that on which the French engineers in 1800 had proceeded, 

 viz. the accumulation of Nile sediment around monuments of a 

 known age. If that depth of sediment be .divided by the number of 

 centuries that have elapsed since the date of the erection of the mo- 

 nument, we obtain a scale of the secular increase of which the base 

 of the monument is zero, assuming that the average increase from 

 century to century has been uniform within an area of some extent. 

 Then if the excavation be continued below the base stone, and the 

 sediment passed through exhibits similar characters as to composi- 

 tion with that above the base line of the monument, it would be fair 

 to apply the same graduation below the zero-point of the scale as 

 above it, and, if we reached so far, we should be able to estimate the 

 time that has elapsed since the first layer of sediment was deposited 

 on the rock forming the channel over which the water spread when 

 it first flowed northward from its sources in the interior of Africa, 



