TRANSACTIONS OF SECTION E. 573 
A terrace formed upon the birth of the Falls shows that they were at first only 
35 feet high. The present height is 158 feet, while the fall along the different 
parts of Niagara River reaches 326 feet. 
During the long earlier history of Niagara there were at first two, and later 
three, separate cataracts. The upper two united when the Falls had receded about 
three miles ; the third joined the others later, but it had no effect on the recession 
of the main falls, as it was soon reduced in height by the backing of the waters 
of Lake Ontario, Until this time, when the Falls had passed the point of union 
by only 600 feet, the volume of the river was 15 per cent. of the present amount. 
It was now increased to its full amount, with the result that the floor of the 
cafion was broken through to a depth of 135 feet. This augmentation resulted 
from the accession of the drainage of Lakes Huron, Michigan, and Superior, which 
formerly drained to the north-east, and only now joined the Lake Erie discharge, 
the change being due to a tilting of the earth’s crust, which culminated only 3,500 
years ago. The upper rapids are due to the river recently reopening a buried 
valley and descending over its eastern slope. This valley, however, did not trend 
northward, but southward. Accordingly, the upper rapids have had little to do 
with the recession of the Falls. 
It thus appears that the rate of recession has been modified by changes of 
volume and of height. These features and the character of the rock-formation, as 
well as the buried valleys, are now known for every furlong which the Falls have 
receded. If we apply the laws of erosion to these changing features the result 
will indicate that the time required for the recession of the first three miles was 
35,000 years, but for the last four miles only 3,500 years, which gives a total age 
of 39,000 years. As all the changing conditions are now known, it appears that 
the probable error does not exceed 10 per cent. This, the author claims, is the 
only computation of their age which has been made upon measurements of all the 
changes in the physics of Niagara Falls. 
4. The Physical Geography of the Ethai Desert of Egypt.) 
By H. T. Ferrar, U.A., F.G.S. 
[PLATE IV.] 
The author exhibited an outline map of the Northern Etbai, which he had 
prepared as an experiment in order to bring out the main physical features of the 
country. It had been traced from more detailed plane-table sheets on the same 
scale (1: 100,000) and adjusted to the chains of triangulation stations which cross 
the country, but many of the details had been omitted. The work of the author's 
colleagues, Drs. Hume and Ball, which should appear on the eastern border of the 
sheet, was also omitted, but could be seen on a smaller sheet (scale 1: 500,000). The 
hill-shading might almost be called diagrammatic, as no attempt had been made 
to depict more than the most important geological and topographical features 
which abound in this hitherto unmapped country. 
Many explorers have made traverses through the deserts, but their maps are 
on rather a small scale, and apart from a few place-names the data were so scanty 
that the whole country has had to be re-explored. Of special interest are the 
following points :— 
1. Basins.—Floyer* has drawn attention to the fact that the wadis draining 
westward from the water-parting are centripetal. The map shows three of these 
basins, viz., Qena, Edfu, and Kom Ombo. 
_ 2, Beheading.—As in South Africa, so here the gentler sloping western wadis 
have been beheaded by the steeper eastern ones, e.g., Rod Um el Farag by Wadi 
Dabur ; Wadi Zeidun by Wadi Dubbagh. 
3. Mushels, i.c., the forking or branching of wadis owing to the ageraded 
' By permission of the Director-General, Survey Department, Egypt. 
2 Quart. Journ. Geol. Sve., vol. xlviii. p. 576. 
