b PROCEEDINGS OF BROOKLYN MEETING. 



to the depth which it did in the case of Long Island sound, where the advance 

 was over a hard rock escarpment. 



As to the dip and strike of the disturbed strata they are found to be too erratic 

 to be of much stratigraphic value, but there is a prevailing strike coinciding with 

 the trend of the moraine, and the strata are either bent into overthrust folds or 

 tilted, with the dip toward the north. North and south anticlines are also met 

 with. At the sides of the harbors on the north shore of Long island the dip is 

 often east or west, apparently due to lateral squeeze or thrust. 



There seems to be but little question as to the competency of ice to produce the 

 phenomena in question, and in this connection the recent experiments by Mr 

 Bailey Willis * are especially apropos. 



As favoring the theory of ice action we therefore have the general structure of 

 the morainal region of the coastal plain ; the uniform coincidence of distorted 

 coastal plain strata with the line of the moraine ; the absence of any distortions 

 where the moraine does not reach the plain ; the much more pronounced distor- 

 tions where the moraine indicates an extensive advance of the ice over the plain, 

 and the prevailing directions of dip and strike. 



The only element which enters into the theory of mountain-making forces as the 

 probable agency which is not also an argument for the ice theory is that of geologic 

 age. The topography of the Marthas Vineyard hills is considered by Professor 

 Shaler to be preglacial. If this be the fact, then the phenomena of dislocation in 

 Marthas Vineyard must be considered as isolated from the remainder of the region 

 and as due to a different cause. The writer failed to see the evidence of it, and it 

 is certainly not the case elsewhere. Thus we find beds of " yellow gravel," the 

 equivalent of the Lafayette formation, included as part of the distorted strata, show'- 

 ing that the disturbance took place subsequent to the period when these gravels 

 were laid down. All authorities are now practically agreed that this formation is 

 at least as recent as the Pliocene, and, considering this fact alone, we should have 

 a very brief period of time in which to develop any preglacial topography. It 

 would imply a very great stress, suddenly and violently discharged— almost in the 

 nature of an eruption in fact— and not a gradual mountain-making process. So 

 far as my experience goes, the facts do not warrant us in assuming that such condi- 

 tions have prevailed. 



Finally, any such development of force would result in the disturbance of strata 

 far below the surface, as well as above, and this we do not find to be the case. As 

 a single example, we may take the exposure at Cold Spring, Long island, where the 

 superficial strata are beautifully folded and crumpled, while the lower ones below 

 the area of ice action are undisturbed. The significant fact should also be remem- 

 bered that the line of disturbance extends in a generally east and west directions 

 instead of north and south— the direction in which experience and observation 

 would lead us to expect that mountain-making forces in this region would be mani- 

 fested. 



On the other hand, the theory of ice action in connection with the continental 

 glacier of the Ice age seems to be both a rational and an adequate one. The fact, 

 are in harmony with it; it enables us to consider the entire area of disturbance as 

 a comprehensive whole, with one series of cause and effect throughout, and not as 



*" The Mechanics of Appalachian structure," extract from the Thirteenth Ann. Rept. of the U.S. 

 Geo]. Survey, 1891-'92, pp. 217-281. 



