AMERICAN GEOLOGY DECADE OF 1870-1879. 



573 



R. D. Irving, 



1873=1879. 



Champlain or Lacustrine epoch, the Second Glacial epoch, inter- 

 Glacial epoch, and first Glacial epoch. This formal announcement of 

 the fact that there had been two distinct periods of glaciation was 

 here made for the first time, although as noted on page 463, Prof. Edward 

 Hitchcock had suggested its possibility as early as 1856. The law of 

 iiowage Chamberlin regarded as essentially similar to that of viscous 

 fluids, in accordance with the observations of Agassiz, Forbes, Tyn- 

 dall, and others. A later study of Greenland glaciers has caused him 

 to change his views on this point. 



Irving, as one of Chamberlin's assistants, dwelt with great detail on 

 the lithological character of the rocks in the regions surveyed by 

 him, and his reports are notable for the beauty of the colored plates 

 of thin sections, which were by far the best that had 

 been prepared and published by an American up to 

 that date. He was assisted in this part of the work 

 by C. R. Van Hise. He also described in some detail the glacial drift, 

 and was the first to announce that the Kettle 

 Range of central Wisconsin was a continu- 

 ous terminal moraine. 



In the third edition of his work on Acadian 

 Geology, which appeared in 1878, Dawson 

 returned once more to a vigorous discussion 

 of the problems of the ice age, and to 

 register again his opposition to the views 

 arenerallv held by American 



Third Edition of fe , . " _ T J 



Dawson's Acadian oeoloffists. MailV of the 



Geology, 1878. & & J 



arguments used closely re- 

 sembled those of his former papers and may 

 be reviewed here for the last time. He re- 

 garded the phenomena of the bowlder clay 

 and drift in eastern America as due to the 

 action of local glaciers, drift ice, and the agency of cold northern 

 currents. Against the theory of an universal glacier he again argued 

 on the ground that such suppositions were not warranted by the facts. 

 "The temperate regions of North America could not be covered with 

 a permanent mantle of ice under existing conditions of solar radiation; 

 for, even if the whole were elevated into a table-land, its breadth 

 would secure a sufficient summer heat to melt away the ice except 

 from high mountain peaks." For the supposition that such immense 

 mountain chains existed and have disappeared, he found no warrant 

 in geology, and for such an "unexampled astronomical cause of refrig- 

 eration" as the earth's passing into a colder portion of space, he found 

 no evidence in astronomy. Against Frankland's idea that glaciation 

 was brought about through a higher temperature of the sea along 

 with a lower temperature of the land, he instanced the actual colder 



Fig. 95.— Roland Duer Irving. 



