Reports and Proceedings — Geological Society of London. 135 



D'Archiac, and the existing Acetabularia, Lamx. Whatever may be 

 the final conclusion respecting the nature of the Archeeocyathinse, 

 their significance as characteristic fossils of Cambrian strata is 

 further manifested by their occurrence, in association with Dorypyge, 

 in Eastern Siberia. 



It may be hoped that the author's anticipations of fresh dis- 

 coveries of fossils in these ancient rocks in the works for the great 

 Siberian railway, now in progress, will be fully realized. 



G. J. H. 



laEIPOE-TS JK.1ST1D :E»iaOGJB3EIDIlsrG-S- 



GEOLOGicAii Society of London. 



I.— January 10, 1900.— W. Whitaker, B.A., F.R.S., President, in 

 the Chair. The following communications were read : — 



1. " On a Particular Form of Surface, the Result of Glacial and 

 Subaerial Erosion, seen on Loch Lochy and elsewhere." By 

 Dr. W. T. Blanford, F.R.S., Treas. G.S. 



This form of surface, first noticed by the author on Lake Como, 

 was afterwards observed in the Great Glen of Scotland and in 

 British Columbia. It consists of an almost even plane sloping at 

 a moderate or high angle, and cut at intervals by small ravines or 

 channels. The sides of the Great Glen have been planed by glacier- 

 action to a greater extent than usual, and between Loch Lochy and 

 Loch Oich, near Laggan, the sides of the Glen have a regular and 

 flat slope of over 35° up to about 1,000 feet above sea-level. Numerous 

 stream-cut channels draining down this slope are, on an avei'age, not 

 more than 10 to 15 feet deep, but some quite exceptional examples 

 may be 50 feet deep ; these channels occupy less than a fourth of 

 the surface. In addition there are larger glens which, although 

 they run out into shallow ravines where they cut the sloping- 

 side of the Great Glen, are frequently 500 feet in depth among the 

 hills. If these wei'e ordinary stream-valleys before the Glacial 

 Period, the cutting away of the ridges separating them to the extent 

 of at least 250 or 300 feet must be attributed to glacial erosion on 

 the sides of the Great Glen. The erosion of the small ravines iu 

 the glacial slope must have been effected by streams in post-Glacial 

 times, and the measurement of their rate of erosion might be 

 expected to throw light on the amount of time which has elapsed 

 since tlie Glacial Period in this district. " The general effect pro- 

 duced by the whole evidence is ... . the small amount of 

 ilenudation that has taken place since the Great Ice Age, and the 

 necessary deduction that no great period of time, measured in 

 years, can have elapsed between the Glacial Epoch and the 

 present day." 



2. " On the Geology of Northern Anglesey." Part II. By C. A. 

 Matley, B.Sc, F.G.S. 



