March 3, 17, & April 3. 1S76.] -^^^ { Trice. 



THE GLACIAL EPOCHS, 



By Eli K. Pbice. 



(^Bead before the American Philoaophical Society, Marcli 3, 17, and April 



3, 1876.) 



The Geologists speak of the Glacial Epoch, with a ready confidence that 

 implies they consider it an admitted doctrine of their science ; and they 

 mean by " the glacial age," one of continental ice sheets. Glacialists have 

 written large volumes on the subject, and its literature is swelling into a li- 

 brary. Agassiz, born and educated among the Alps, studied their glaciers 

 and their effects, and traveling thence, applied his theories to other parts of 

 the world. He was very sincere in his convictions, and complained that so 

 few of his colleagues accepted his views ; but in the confidence that he 

 held a great truth he was willing to abide the coming of the time he fore- 

 saw, when Geologists would generally accept his theory. That time 

 seemed to have arrived before he died, with some distinguished exceptions.^ 



Those who have made Geological Surveys of England and Scotland, 

 and parts of the Continent of Europe, either as conductore of public Sur- 

 veys, or as Professore in colleges, or teachers through the press, find the 

 ready explanation of what they see, in the doings of the great Glacial 

 Epoch, when the supposed Northern ice-sheet filled the Arctic Ocean, the 

 British and Irish Seas, and covered Northern Europe continuously over 

 land, rivers, seas and mountains, to shed its icebergs far out into the Atlantic. 

 And so too in this broad country, the Geologists who have made our public 

 Surveys, w^ho teach in our colleges, or publish, have generally read the 

 rocks and drifts in the same way, in making explorations that have ex- 

 tended over the length and breadth of this continent. 



Geologists, as other scientists, must follow the truth as the facts of nature 

 compel them. Truth's compulsion is as inexorable as the pressure of the 

 gigantic ice-sheets, these glacialists suppose, bore down from the pole. But 

 they, as others, must often review their facts before they accept a theory as 

 conclusive, and make themselves sure that they have not, by an engrossing 

 attention to limited fiicts, overlooked others which should have influenced 

 their theorizations. 



They teach that the Glacial Epoch has occurred twice at least, since the 

 rocks were laid in the strata as we see them ; long after the coal measures 

 were formed ; of which the evidence is to be found upon the surface of the 

 rocks as they now exist, and in the clays, and drifts, and boulders now spread 

 over those rocks. Geologically speaking, these phenomena are of recent 

 date, althougli before the Niagara began to cut the channel we now see. 

 The astronomical cause assigned for them gives them a periodicity of about 

 twenty-one, to twenty-two thousand years, and our northern hemisphere the 

 respite of the half of such period, before it shall again be ground into paste. 



PROC. AMEB. PHILOS. SOC. XVI. 97. 2e 



