134 NEW YORK STATE MUSEUM 



Therefore, the unconformity is complete and as striking a thing as is 

 to be found between any ancient crystalline series and later sedi- 

 ments. 



On the south side opportunity is seldom found to inspect the 

 intimate relations of the schist-limestone-quartzite series with the 

 banded gneisses that lie below. Simple undisturbed beds are almost 

 never seen exposed at the surface. In only two places may one 

 see something of the structural relation, and these exposures 

 are somewhat confused and obscured by erosion and cover. .Neither 

 of them lies within the quadrangle under discussion. One is at 

 Ossining in the Tarrytown quadrangle and the other at Hastings in 

 the Harlem quadrangle. Both show unusually good development of 

 quartzite for the south side series, and as nearly as one may judge 

 from the attitude of beds at the present time, it is conformable 

 to the general structure of the gneisses. No better evidence than this 

 of the relation on the south side is at hand, except as exposed in 

 certain pieces of engineering work still farther to the south and east. 



One of these is at Vahalla in the Tarrytown quadrangle where the 

 surface drift was entirely stripped from the contact on the site of the 

 new Kensico dam. Other occurrences are in New York City, in the 

 Harlem sheet, in deep tunnels, one crossing the contact between 

 gneiss and limestone under the Harlem river at 167th street, New 

 York City, and the other under Delancey street in lower Manhattan, 

 where the same relations were exposed in the city tunnel of the 

 Catskill aqueduct. The striking thing about all three of these occur- 

 rences is the apparent conformity of the bedding in the Inwood 

 limestone with the structure of the underlying gneisses, the quartzite 

 being absent in all these places. Photographs have been taken of 

 this contact and inspection has been made with great care. The best 

 that can be said is that the structure is apparently conformable and, 

 in the best occurrence of all, that under Delancey street, the structure 

 is especially plain and the conformity practically perfect. In none 

 of these cases is there deformation of sufficient consequence to 

 obscure the relation and certainly no deformation of the usual sort 

 could have brought about this parallelism of structure. It is difficult, 

 to say the least, to find a satisfactory explanation for this apparent 

 conformity other than the very obvious one that the beds are in 

 reality conformable. One could readily believe that, in an occasional 

 spot, the structure of the Precambrian rocks might accidentally 

 coincide with that of the overlying series and be misleading, but 

 it is past belief that all of them should be misleading. 



