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, N. J., so that the presence of cretaceous material, 
as well as pre-glacial drift, could readily be accounted for 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 archean 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 Cardium 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 may be readily 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 study. 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 
archean ridge; nevertheless, as we have seen, they appear at the 
surface, not more than. two miles distant, in a southeasterly direc- 
