GEOLOGY OF THE WEST POINT QUADRANGLE, NEW YORK 1 45 



of such material is to be seen now, and none is to be seen elsewhere 

 north of the Highlands. 



Certain islands within the present channel of the Hudson river, 

 such as Constitution island, lona island and several small ones, 

 however, are believed to have a genetic connection with this missing 

 history. It is argued, for example, that the river channel at first 

 passed to the south of lona island instead of the north side where 

 it is now, and that this channel was established previous to one of 

 these deposition epochs. During that time deposits were laid down 

 filling the gorge, and when rejuvenated the river lodged on the 

 opposite side of the valley from its former position, becoming 

 entrenched there so firmly in the soft deposits that it has held 

 that position ever since Even when the hard rock was reached 

 it kept the new position and the islands have resulted from 

 continued erosion. No better explanation has been given of the 

 origin of several such islands in the Hudson gorge and no equally 

 good structural reason independent of some such history is oflfered. 



So far as the features of this quadrangle are concerned, therefore, 

 little direct evidence of oscillation and former occupation of the 

 ground by Tertiary deposits is to be seen, but the indirect evidence 

 of the islands within the inner gorge is at least worth considering 

 in support of such history. 



Glacial modification. Glacial scour has accomplished more in the 

 Hudson gorge than at most other places and perhaps some of the 

 change of course as well as form is due to that agent. It has already 

 been pointed out in connection with the discussion of the Storm 

 King crossing of the Catskill aqueduct that glacial over-deepening 

 and widening of the gorge has been proved at that point. It may 

 very well be that glacial ice not only enlarged certain places which 

 formerly were much more restricted, but that, at the time of with- 

 drawal, it also left obstructing drift in portions of former channels 

 that were previously open. Thus it may be that the change of course 

 in the case of some of these islands is glacial and postglacial rather 

 than Tertiary. The history at least with regard to some of these 

 islands is obscured by glacial scour and glacial deposits and it may 

 be that the position of the river is exactly reversed by this latet 

 experience quite independently of the earlier modifications. The 

 present profile on such a spur as Anthony's Nose is good proof 

 also of glacial modification of form. This prominent projecting mass 

 has been snubbed by glacial ice. 



