BULLETIN OP THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 19, pp. 347-366 November io, i908 



GLACIAL PEEIODS AND THEIR BEARING ON GEOLOGICAL 



THEORIES^ 



BY A. P. COLEMAN 



[Presented before the Society December 30, 1907) 



CONTENTS 



Page 

 Introduction 347 



The Pleistocene glacial period 348 



The Permo-Carbonif erous glacial period 349 



The early Cambrian glacial period 353 



The Lower Huronian glacial period 3.55 



Interglacial periods in the Pleistocene 35G 



Interglacial periods in ancient ice ages 359 



Conclusions . . , 3G2 



Introduction 



It is intended in this paper to call attention to certain sides of glacial 

 geology which have a bearing on the broader problems of geology in gen- 

 eral, and which should receive consideration from workers in other de- 

 partments of geology and in the related sciences which deal with the early 

 history of the earth, such as physics and astronomy. Glacial geolog}' 

 will be construed in its widest sense, not as confined to Pleistocene phe- 

 nomena, but as including glacial activity in all ages where ice has left 

 widespread proofs of its work. 



It will be necessary to give a summary of the evidence showing the 

 extent of glaciation at various times in the earth's history ; and the ques- 

 tion of interglacial periods will be taken up briefly also. Afterward 

 general conclusions will be drawn from the evidence, and these will be 

 used as tests of various theories. 



Evidence of ice action on a large scale is, of course, widely available 

 in regard to the Pleistocene ice age, from which the world seems to be 

 just emerging and whose broad efl'ects all geologists admit. Such evi- 



1 Manuscript received by the Secretary of the Society March 25, 1908. 



XXXIV— Bull. Geol. Soc. Am., Vol. 19, 1907 (347) 



