ICE INVASION AN AGENT OF DEFORMATION. 349 



vigorous glacial currents enabled large portions of the englacial drift to 

 be carried to the glacial boundary and heaped in these hills, knolls and 

 irregular ridges ; other portions formed the kames and eskers ; and a con- 

 siderable stratum of the general till-sheet appears to have been englacial 

 and at last superglacial ^vhen the rapid ablation bared the land surface 

 and permitted that part of the drift to fall upon it as the upper division 

 of the till. 



DISPLACEMENT AND FOLDING OF SOFT UNDERLYING BEDS. ♦ 



Closely associated with the outermost moraine along a distance of more 

 than 200 miles on Staten and Long islands, Block island, Marthas Vine- 

 yard and Nantucket, the soft Cretaceous and Tertiary strata underlying 

 the morainic drift have been more or less disturbed, being seen in many 

 sections to be pushed into anticlinal and synclinal folds parallel with 

 the course of the moraine. Mr Arthur Hollick, in a paper read before 

 the last sunnner meeting of this Society, accounts for this displacement 

 and folding by the great pressure of the ice-sheet at a time of its bodily 

 advance b}^ which the moraine was amassed.* In this conclusion he 

 agrees with the earlier statement of the same explanation by F. J. H. 

 Merrill for sections observed by him on Long island, t and with the 

 present writer for the remarkably folded strata of Gay Head, at the west 

 end of Marthas Vineyard, and for the less inclined early Pleistocene fos- 

 siliferous marine beds under the moraine in Sankoty head, on the east 

 shore of Nantucket. X 



These disturbances of soft and easily dislocated beds beneath the drift 

 of an ice incursion are equalled or perhaps surpassed by the dislocation, 

 crumpling and infolding with glacial drift, which similar underlying 

 strata display on the islands of Moen and Riigen, in the southwest part 

 of the Baltic sea. Doubtless there, as on our Atlantic coast, the ice-front 

 advanced, and the very irregular displacements and folds are effects of 

 its disrupting power. 



When any ice incursion took place upon harder rocks, as in the coun- 

 try westward from Staten island to the driftless area of Wisconsin, the 

 pressure in many places may have been equally great, but it was ex- 

 pended in eroding, planing and striating the bed-rocks, as they are found 

 everywhere within the limit of the outermost prominent moraines. The 

 extent of the ice advance, however, Avhich formed these moraines and 

 l»r()duced the folds of the soft strata eastward and the glaciation of the 

 bed-rocks westward, may probably have been no more than a few miles or 



• Bull. Geol. Son. Am., this volume, pp. 5-7; more fully puhlislicrj, with sections of the distorted 

 and foMed beds, in Trans. New York Aead. Sei., vol. .xiv, OctoVtor, 18!>4, pp. 8-20. 

 t Annftls of the New York Acad. Nat. Sci,, vol. iii, \hhi;, pp. 341-304, with seetions .in<l map. 

 t Proc. Bo»t. Soc. Nat. Hist., vol. xxiv, 1888, p. \Xt. 



