228 Royal Society. 



9. That in nearly every part of the ground penetrated, artificial 

 substances have been found, such as fragments and particles of burnt 

 brick and pottery, and at the lowest depth reached. 



The author then enters, at some length, into the circumstances 

 which modify the deposition of the sediment in different parts of the 

 valley, showing how the coarser and heavier matter held in suspen- 

 sion in the inundation water must be deposited in greatest amount 

 in the higher parts of the river's course, in its bed, and near its 

 banks ; that this must be further caused by the slight fall, which 

 between Assouan and Cairo is less than 6 J inches in a mile, the Nile 

 in its whole course from the first cataract to the sea not being used 

 as water power ; that the vast heat must cause an evaporation that 

 lets fall the solid matter more abundantly in the southern latitudes ; 

 that the river from 42 miles below the first cataract is nowhere 

 allowed to overflow the land, but is confined by embankments, so 

 that the waters of irrigation are spread by canals, by which and by 

 the irregularities of the ground eddies are formed. From all these 

 causes affecting the distribution of the sediment over the land, the 

 depth of the annual deposit by the inundation is very different in 

 different parts of the valley, and consequently the same lapse of 

 time may be represented by very different depths of the soil. 



The author next treats of the rate of secular increase of the allu- 

 vial land. Before entering upon the results at which he arrives by 

 these recent researches, he refers to the operations of the French 

 engineers at the end of the last century, who state the mean of the 

 rise of the land between Assouan and Cairo to be 5 inches in a cen- 

 tury. From that conclusion, and especially from the application of 

 it, the author dissents, and states his reasons at considerable length 

 in the Appendix to his Memoir. He considers that in every situa- 

 tion where a calculation is to be made of the rate of secular increase, 

 •we must have a fixed point in time to start from ; that is, the known 

 age of a moimment, the foundation of which rests vxpon Nile sedi- 

 ment, and upon the sides of which the latter has accumulated by sub- 

 sequent inundations. If there have been no local causes to disturb 

 the probabihty that the sediment above and below the foundation 

 has accumulated at the same rate, we divide the amount above 

 the foundation by the number of centuries known to have elapsed 

 from the erection of the monument to the present time, and then 

 apply the same chronometric scale to the greatest ascertained depth 

 of sediment below the foundation. Estimated by this rule, the re- 

 searches at HeHopolis gave the result of a rate of increase of 3-18 

 inches in a century. But a degree of uncertainty arises at this place, 

 because of the city appearing to have been built upon a portion of 

 land somewhat raised above the level of the rest of the skirt of the 

 desert, and advancing into the low ground then inundated by the 

 Nile ; whereby it became doubtful whether a bed of sand penetrated 

 was sedimentary or a part of the desert land. 



In the excavations near the colossus of Ramesses II. at Memphis, 

 there were 9 feet 4 inches of Nile sediment between 8 inches be- 

 low the present surface of the ground and the lowest part of the 

 platform on which the statue had stood, after making a due allow- 



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