4G6 Royal Society. 



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, 

 subject however to correction for causes that might make a differ- 

 ence in the rate of increase between the earlier and later periods. 



The author submitted his scheme to the President and Council of 

 the Royal Society, who encouraged his proceeding by acceding to 

 his request of a grant from the Donation Fund at their disposal, to- 

 wards the expenses of the researches. 



The author introduces his subject by a sketch of the physical 

 geography and geology of Egypt, a description of the annual inun- 

 dations, and of the sediment deposited from the water of the Nile. 



Egypt is separated from Nubia by a low hilly region, about fifty 

 miles broad from north to south, chiefly composed of granitic rocks, 

 but associated with two kinds of sandstone, the one belonging to 

 the cretaceous series, the other of the newer tertiary age. The 

 valley of Upper Egypt is bounded by two ranges of hills running 

 northward, the Arabian range on the right, the Libyan on the left 

 of the river, both alike composed of sandstones and limestone. The 

 cretaceous sandstone extends from the granitic rocks forming the 

 first cataract at Assouan for about eighty-five miles, where it is 

 covered by a limestone which has the characters of the upper chalk 

 of Europe. This chalk continues on both sides of the valley for 

 about 130 miles, when it is covered in its turn by a tertiary num- 

 mulite limestone, and of which the further prolongation northward 

 of both ranges is composed; this nummulite limestone can be well 

 studied in the extensive quarries of Gebel Mokattam above Cairo, 



The author briefly describes the operations of the private associa- 

 tion of English, French, and Austrian Engineers in 1846-47, com- 

 monly called the French Brigade, for the purpose of determining the 

 disputed question of the relative levels of the Red Sea and Medi- 

 terranean. The French engineers, at the beginning of the present 

 century, had come to the conclusion that the Red Sea was about 30 

 feet above the Mediterranean, but the observations of Mr. Robert 

 Stephenson, the English engineer, at Suez, of M. Negretti, the 

 Austrian, at Tineh near the ancient Pelusium, and the levellings of 

 Messrs. Talabot, Bourdaloue and their assistants, between the two 

 seas, have proved that the low-watermark of ordinary tides at Suez 

 and Tineh is very nearly on the same level, the difference being, 

 that at Suez it is rather more than one inch lower. 



At the island of Phila% about five miles above Assouan, may pro- 

 perly be placed the first entrance of the Nile into Egypt. It is here 

 about two miles broad, but is soon after divided into several branches 

 by the rocks that rise up in its bed to form the rapids, commonly 

 called the First Cataract, which have^a descent of about 85 feet in a 



