324 FRA NK B URSLE V TA YL OR 



of the ice-front in that region was not by an even, steady move- 

 ment giving a uniform rate of recession, but by oscillations in 

 which there were many alternating episodes of relatively rapid 

 retreat and less marked readvance separated by times of halting, 

 when the ice-front remained for some time in a stationary state. 

 These minor oscillations with repeated haltings characterized the 

 whole of the main movement of retreat of the last ice-sheet in 

 the West. Each halt was the occasion of the building of a 

 frontal or marginal moraine, and the drift of the Wisconsin 

 epoch is nearly everywhere marked by a numerous series of 

 these recesno7ial moraines. 



HISTORICAL. 



In the East the ice-sheet was long thought to have had a 

 different habit, and to have made no recessional moraines like 

 those of the West. The two great marginal moraines extending 

 westward along the coast from Cape Cod and Nantucket Island, 

 and converging toward the west end of Long Island, have been 

 known for many years.' The extension of one of these as the 

 so-called "terminal moraine" of H. Carvill Lewis, having a 

 general course west-northwest across New Jersey and Pennsylva- 

 nia, is also well known. ^ These, however, are not recessional 

 moraines, but the frontal deposits of the grand climax, when the 

 ice -front rested after the general advance and before the general 

 retreat. 



Leverett has mapped the recessional moraines of the extreme 

 western portion of New York and of the northwestern part of 

 Pennsylvania, and he has also mapped in detail the morainic 

 deposits of the Olean and Salamanca quadrangles in western 

 New York. The folios to which these belong have not yet been 

 published, but a map of the Olean quadrangle has been issued 



' Warren Upham, " Terminal Moraines of the North American Ice Sheet," Am. 

 Jour. Sci., Ill, Vol. XVIII (1879), pp. 81-92, 197-209. 



^George H. Cook, "On the Southern Limit of the Last Glacial Drift Across 

 New Jersey and the Adjacent Parts of New York and Pennsylvania," Am. Inst. 

 Min. Eng. Trans., Vol. VI (1879), pp. 467-520; H. Carvill Lewis, "Report 

 on Terminal Moraine Across Pennsylvania and Western New York," Second Geol. 

 Surv. of Penn.^ Rept. Z., 1884. 



