1892.] NEW YORK ACADEMY OF SCIENCES. 101 



until it again slopes to the waters of Staten Island Sound on the 

 other side of the island. This section would cross directly through 

 the clay beds at Kreischerville, and if extended would cross those 

 at Woodbridge, X. J., so that the presence of cretaceous material, 

 as well as pre-glacial drift, could readily be accounted fur at Prince's 

 Bay, on the theory of glacial transportation, and the same might also 

 be said in regard to the material at Tottenville. If, however, we con- 

 sider the conditions at Arrochar, we shall see that no such explanation 

 is probable. A section across the island from this locality, in the same 

 direction as before, soon strikes the archsean ridge, beyond which no 

 cretaceous strata are known, so that whatever cretaceous material we 

 may find at Arrochar must be either in place or else be derived from 

 the immediate vicinity. Recent excavations have greatly assisted in 

 the solution of the problem, and I was fortunate enough to arrive 

 there one day when a fresh section was exposed. This showed at the 

 base a layer of sandy micaceous clay containing concretions of limo- 

 nite, next a layer of yellow sand and gravel, then about four feet of 

 modified drift, and finally bowlder drift on top — a series similar in 

 arrangement and material to those at Tottenville and Prince's Bay. 

 In the strata of clay and overlying yellow sand I found specimens 

 of Gardium dumosum, and in the gravel above were silicified corals 

 characteristic of the pre-glacial drift. The entire series dips at an 

 angle of about forty degrees towards the northwest. 



That this stratified material has been subjected to considerable 

 disturbance since it was originally laid down, is evident from the 

 position in which we now find it. It is many feet vertically out of its 

 normal position, and laterally the disturbance has been such as to 

 transform a gradual dip of about 50 feet per mile towards the south- 

 east into a steep dip in the opposite direction. The vertical dis- 

 placement ma}^ be readilv accounted for, at least in part, by the 

 well-recognized elevation which occurred in this region since the 

 period of glaciation. The lateral displacement, however, offers an 

 interesting field for studv. The indications are that the beds have 

 been squeezed and distorted by the lateral pressure of the ice sheet 

 advancing from the northwest. The exposure on the north side of 

 the Fingerboard Road, previously mentioned, shows well-marked 

 indications of this action. The layers of sand and clay here have 

 been bent into a distinct monoclinal fold, with concretions lying flat 

 in the plane of the bedding throughout the entire fold. I am also 

 inclined to attribute the elevation of this region in part to the pres- 

 sure exerted by the ice front as it advanced over the archaean 

 ridge, and then descended with a sheer drop of some 250 feet upon 

 the plastic cretaceous strata at the base. These were either eroded 

 to a great depth, or else squeezed up and shoved ahead of the ice sheet. 

 They are not indicated at the surface, and, as far as I am informed, 

 have not been reached in any well-borings near the base of the 

 archaean ridge; nevertheless, as we have seen, they appear at the 

 surface, not more than two miles distant, in a southeasterly direc- 



