94 Reports and Proceedhujs — Geological Socief;/ of London. 



years. As the Niagara Limestone is thinner at the month of the 

 Gorge, and the Clinton Limestone has dipped ont of sight at the 

 "Whirlpool, there is nothing in the stratigraphy to indicate a slower 

 recession in the past than in the present. Moreover, nearly one-third 

 •of the erosion has heen accomplished b}' two pre-Glacial streams, one 

 from the south and a smaller one from the north. Therefore the 

 author concludes with considerable confidence that the Gorge is less 

 than 10,000 years old, and that the ipe of the Glacial epoch continued 

 down to that time, to such an extent over the lower St. Lawrence 

 Valley and Central New York that it obstructed the entire eastern 

 drainage of the Great Lakes. 



There is nothing which would lead to a longer estimate of the time 

 which has elapsed since the Kansan stage of the Glacial epoch than 

 that approved by Professor Calvin, of Iowa, and agreed to by Professor 

 Winchell. These assume 8,000 years as the limit for post-Glacial 

 time, and that a multiple of this by 20, amounting to 160,000, would 

 carry us back to Kansan time. This, however, would still leave as 

 long a period still earlier, for the advance of the ice. The author's 

 impression is that the whole epoch may well have been compassed 

 within 200,000 years. 



2. " On the Application of Quantitative Methods to the Study of the 

 Structure and History of Hocks." Bv Henry Clifton Sorby, LL.D., 

 P.R.S., r.L.S., F.G.S. 



The knowledge of the final velocities of material subsiding in water is 

 of fundamental importance ; but the relation between size of particles 

 and velocity is complex, and perhaps may be partly explained by 

 a thin, adherent film of water. The angle of rest in the case of sand- 

 grains of varying size and quality enables us to ascertain approximately 

 the velocity of current necessary to keep such sand drifting, and that 

 needed to move it when at rest. The comparison of this angle with 

 that observed in sedimentary rocks made of similar materials may be 

 used to determine the amount of vertical contraction of rocks since 

 deposition, the average in cases studied in Tertiary and Secondary 

 rocks being from 100 to 57. In studying the drifting of sand along 

 the bottom by currents (on which the author experimented in a small 

 stream many years ago), the results are found to varj-, according to 

 whether the water is depositing sand as well as drifting it, and 

 according to whether ripples are or are not being formed on the 

 bottom. The velocity of a current can be determined approximately 

 in feet per second for different kinds of sand. The connection between 

 the structure of ' ripple-drift ' and time is discussed ; and an equation 

 is given, from which the rate of deposit in inches per minute can be 

 deduced. The connection between the structure of a deposit and 

 depth of water is found to be difficult to study quantitatively. Prom 

 the occurrence of ' drift-bedding ' the depth of water may probably be 

 determined to within a few feet, and on this being applied to 

 particular rocks some interesting results come out, including the 

 separation of sandstones into several different groups. The deposition 

 of fine deposits, like clay, is a most complex subject, varying according 

 to the amount of mud present in the water, and according to whether 

 the grains subside separately or cohere together. When no pressure 



