HYPOTHETIC CONTINENTAL OSCILLATIONS. 203 



adjacent areas, I was led thirteen years ago to the belief that the Ice age 

 comprised two or more glacial epochs ; but within the past year I have 

 been gradually returning to the opinion which I previously held while 

 engaged with Professor C. H. Hitchcock on the New Hampshire geolog- 

 ical survey, that the Pleistocene glaciation was essentially a unit.* 



Other evidences which have been regarded by Chamberlin, Salisbury, 

 and McGee, as indicative of a long interglacial epoch, drawn from the 

 Pleistocene erosion of the Mississippi river, the Ohio and its tributaries, 

 the Susquehanna and other rivers of the Atlantic slope, appear to me to 

 admit a different interpretation. As I see the late Pliocene and Pleisto- 

 cene history of this region, a great uplift of the continental plateau closed 

 the Tertiary era and ushered in the Quaternary. During a long time 

 the land stood at a high altitude, and in the earlier part of this time the 

 Lafayette gravel and sand beds were deposited by the rivers eroding the 

 mountain and highland portions of their basins and spreading these beds 

 in their larger valleys and on the coastal plain ; but before the elevation 

 attained its maximum, causing the Pleistocene ice accumulation, the 

 streams, no longer overloaded in proportion to their steeper descent, had 

 eroded large portions of the Lafayette formation. By the ice weight the 

 earth's crust at last was depressed, so that when the ice-sheet in the Mis- 

 sissippi valley reached its farthest limit it was bordered by a shallow 

 lake, into which the fine silt of the glacial streams was carried and de- 

 posited as loess, upon which higher portions of the loess were afterward 

 brought by river floods. According to this view, the glacial period there 

 appears to me to have been continuous, with retreats and reJidvances of 

 the ice-front, but without division by long interglacial epochs. This 

 opinion, however, is put forth in no criticising or dogmatic spirit, but 

 with a sense of my obligation to present the results of my studies, in 

 which I am surely as liable to err as others, for the discovery of the 

 Pleistocene history of our continent. 



Probable Synchronism of Glaciation in North America and Europe. — The 

 glacial drift of Europe also seems to me, after reading and pondering 

 Professor James Geikie's recent very able paper arguing for five glacial 

 epochs there.f to be more probably referable to one epoch of continuous 

 but fluctuating glaciation, which appears, by a comparison of the Post- 

 glacial oscillations of the Scandinavian peninsula and of our northeastern 

 Atlantic coast, to have been at least approximately synchronous with 

 the Glacial period in America.^ On both continents it has been com- 



*For arguments sustaining this view, see Professor G. F. Wright's paper, "Unity of the Glacial 

 Epoch," Am. Jour. Sei., Ill, vol. xliv, pp. 351-373, November, 1892. 



f'On the Glacial Succession in Europe," Trans. Roy. Soc. Edinb., vol. xxxvii, pp. 127-140, with 

 map, May, 1892. 



| Bull. Geol. Soc. Am., vol. iii, 1892, pp. 508-511. 



