122 Gregory — Progress in Interpretation of Land F 



or wis. 



Canada and the extent of glacial cover revealed. Fol- 

 lowing 1875 the pages of the Journal contain many con- 

 tributions dealing with the origin and structure of 

 moraines, eskers, kames, and drumlins. Before 1890 

 twenty-eight papers on the glacial phenomena of the Erie 

 and Ohio basin alone had appeared. By 1900 substantial 

 agreement had been reached regarding the significant 

 features of the drift, the outline history of the Great 

 Lakes had been written, and the way had been paved for 

 stratigraphic studies of the Pleistocene, which bulk large 

 in the pages of the Journal for the last two decades. 



Epochs of Glaciation. 



For a decade following the general acceptance of the 

 glacial origin of "diluvium," the deposits were embraced 

 as "drift" and treated as the products of one long period 

 of glacial activity, and throughout the controversy of 

 iceberg and glacier the unity of the glacial period was 

 unquestioned. Beds of peat and fossiliferous lacustrine 

 deposits in Switzerland, England, and in America and 

 the recognition of an "upper" and a "lower" diluvium 

 by Scandinavian geologists suggested two epochs, and as 

 the examples of such deposits increased in number and 

 it became evident that the plant fossils represented forms 

 demanding a genial climate and that the phenomena 

 were seen in many countries, the belief grew that minor 

 fluctuations or gradual recession of an ice sheet were 

 inadequate to account for the phenomena observed. 



It is natural that this problem should have found its 

 solution in America, where the Pleistocene is admirably 

 displayed, and where the State and Federal surveys were 

 actively engaged in areal mapping. In 1883 Chamber- 

 lin 60 presented his views under the bold title, "Prelim- 

 inary Paper on the Terminal Moraine of the "Second 

 Glacial Epoch," and the existence of deposits of two or 

 more ice sheets and the features of interglacial periods 

 were substantially established by the interesting debate 

 in the Journal led by Chamberlin, Wright, Upham and 

 Dana. 61 Contributions since 1895 have been concerned 

 with the degree rather than the fact of complexity, and 

 continued study has resulted in the general recognition 

 of five glacial stages in North America and four in 

 Europe. 



