284 Geological Society : — 



3. " On Tertiary Cyclostomatous Bryozoa from New Zealand." 

 By Arthur W. Waters, Esq., F.G.S. 



May 25.— Prof. J. W. Judd, F.R.S., President, m the Chair. 

 The following communications were read : — 



1. " On the Eemains of Fishes from the Keuper of Warwick and 

 Nottingham." By E. T. Newton, Esq., F.G.S. ; with Notes on 

 their Mode of Occurrence by the Rev. P. B. Brodie, M.A., F.G.S., 

 and E. Wilson, Esq., F.G.S. 



2. " Considerations on the Date, Duration, and Conditions of the 

 Glacial Period with reference to the Antiquity of Man." By Prof. 

 Joseph Prestwich, M.A., F.R.S., F.G.S. 



After showing how the discoveries in the valley of the Somme and 

 elsewhere, 28 years ago, led geologists who had previously been dis- 

 posed to restrict the age of man, to exaggerate the period during 

 which the human race had existed, the author proceeded to discuss 

 the views of Dr. Croll on the date of the Glacial epoch. Dr. Croll, 

 who had at first referred this to an earlier phase of orbital eccen- 

 tricity, commencing 980,000 years ago, subsequently regarded it as 

 coinciding with a minor period of eccentricity that commenced 

 240,000 and terminated 80,000 years since. This last estimate was 

 chiefly supported by the amount of denudation that had subsequently 

 taken place. 



The efficacy of the increased eccentricity of the earth's orbit in 

 producing the cold of the Glacial epoch was shown to be very 

 doubtful ; for as similar changes in the eccentricity had occurred 

 165 times in the last 100 millions of years, there must have 

 been many glacial epochs in geological times, several of them much 

 more severe that of the Pleistocene period. But of such glacial 

 epochs there was no valid evidence. Another inference from Dr. 

 Croll's theories, that each glacial epoch consisted of a succession of 

 alternating cold and warm or interglacial phases was also questioned, 

 such alternations as had been indicated having probably been due 

 to changes in the distribution of land and water, not to cosmical 

 causes. The time requisite for such interglacial periods as were 

 supported by geological evidence was more probably hundreds than 

 thousands of years. 



Recent observations in Greenland by Professor Helland, Mr. V. 

 Steenstrup, and Dr. Rink, had shown that the movement of ice in 

 large quantities was much more rapid, and consequently the denu- 

 dation produced much greater than was formerly supposed. The 

 average rate of progress in several of the large iceberg-producing 

 glaciers in Greenland had been found to be 36 feet daily. Applying 

 these data and the probable accumulation of ice due to the rainfall 

 and condensation to the determination of the time necessary for the 

 formation of the ice-sheet, the author was disposed to limit the 

 duration of the Glacial epoch to from 15,000 to 20,000 years, in- 

 cluding in this estimate the time during which the cold was in- 



