Geology and Mineralogy. 71 



sion of the land on which it lay, and to have witnessed, during 

 the retreat and removal of its load, a progressive re-elevation of 

 the same area to its present height. 



"For Europe, also, after reading the recent very ably written 

 ai'ticle by Prof. James Geikie,* in which he argues for five dis- 

 tinct epochs for glaciation, I think that there, as here, it is more 

 reasonable to refer the whole of the glacial drift to a single glacial 

 epoch, with moderate fluctuations in the extent of the ice-sheets 

 and glaciers. In thus differing from this eminent glacialist and 

 from Wahnschaffe in Germany, Penck in Austria, and DeGeer 

 in Sweden, who are of the same opinion with Geikie, that there 

 were long mild interglacial epochs in Europe, I come into agree- 

 ment, on this question, with other distinguished European glacial- 

 ists, as Lamplugh in England, Falsan in France, and Hoist in 

 Sweden, who hold that the Quaternary reign of ice was essentially 

 a unit. But this present state of our division under the two 

 opinions surely calls for much further observation and candid 

 study that ultimately the truth may be confidently known, on 

 whichever side it may be." 



2. The Pleistocene History of Northeastern Iowa, by W. J. 

 McGeb, pp. 189-757 of the 11th Report of the Director of the 

 U. S. Geological Survey for 1889-90. — This paper by Mr. McGee 

 consists of a very comprehensive discussion of the topography, 

 soils, rivers, glacial deposits, and glacial history of northeastern 

 Iowa. The author has presented his views in former volumes of 

 this Journal, the latest in volume xxxv (1888). The present 

 report gives his final results in detail and with numerous illustrat- 

 ing plates and maps. His general conclusions as to the glacia 

 invasions are as follows: Over about half of Northeastern Iowa 

 16,500 square, miles in area, there are two well-defined moraine 

 deposits, indicative of two ice-invasions ; through nearly half of 

 the rest, loess overlies the two deposits, and in a small area, only 

 one of the two, and occurs over the driftless area on the borders 

 of Wisconsin, and along the borders of the Mississippi farther 

 south. Above the lower or older moraine deposit there is gene- 

 rally a bed of soil abounding in sticks, stems and other remains 

 of trees, indicating that a forest growth covered much of the 

 region of the lower moraine before the deposition of the upper ; 

 and besides the soils, there are locally stratified beds of sand. 

 The two lobes of ice which moved southwestward either side of 

 the driftless area during the second invasion, are stated to have 

 occasioned, by their junction below, a large ice-bound lake — 

 Lake Hennepin as named by the author; and within this lake 

 most of the loess of Iowa was deposited. The loess contains 

 freshwater and land shells, as elsewhere, and makes the most 

 fertile land of the region. But the shells are much less than their 

 normal size, owing, it is observed, to the coldness of the 

 waters. " The third invasion by the ice fell short of this terri- 

 tory." 



* " On the Glacial Succession in Europe," Trans. Royal Society of Edinburgh, 

 vol. xxxvii, pp. 127-149, with map, May, 1892. 



