ROGERS, GEOLOGY OF THE CORTLAXDT SERIES 53 



in the district and are of especial interest from the standpoint of contact 

 action. They were first noticed by Dana, who mapped 39 several of the 

 larger limestone areas in the western part of the district. They appear 

 to be most frequent in this area; in the region around Salt Hill they 

 occur less commonly. In the main diorite area, however, they are much 

 more numerous than is indicated on the map ; there are many, especially 

 near Crugers, that are too small to be shown ; and near Salt Hill, they are 

 too small and their relations too obscure for adequate representation on 

 the map. 



Dana maps three inclusions of limestone in the large diorite area, and 

 all of these have been found by the writer to be a very quartzose schist, 

 closely resembling limestone in appearance, but nevertheless of an entirely 

 different composition. Either Dana, who was looking for limestone, 

 mistook its identity on account of its peculiar appearance, or else it* does 

 contain calcareous layers which he happened to find and which the writer 

 overlooked; but it is certain that it is essentially a quartz schist. It 

 weathers in layers, however, which also tends to give it the appearance of 

 limestone. It appears to be chiefly quartz in most places, with some 

 feldspar and traces of muscovite ; but it occasionally contains layers which 

 are entirely similar to the Manhattan schist. It is usually considerably 

 decomposed. In one case, it resembled a very fine gneiss, but other parts 

 of the same inclusion were normal, and it was moreover very similar to 

 an outcrop of schist on Broadway, the straight road running north from 

 Verplanck. An outcrop of the schist (see map) is to be seen on the post- 

 road, a short distance below Montrose, and the cliff behind Mackey's store 

 at Buchanan contains two stringers of this rock imbedded in a somewhat 

 gneissoid diorite, which to the west becomes pyroxenite (Plate III, fig. 2). 



The inclusions are generally associated with rocks which show more or 

 less evidence of metamorphism. This is so apparent that these rocks 

 were first interpreted by the writer as parts of the schistose inclusions 

 themselves, but their peripheral position would seem to indicate that they 

 are true igneous rocks which have undergone some shearing; and this is 

 borne out by the composition, which is that of a mica diorite. The 

 strongly crushed gabbro is also found on the border of two of these in- 

 clusions. 



The abnormal mineralogy of the schist is peculiar, although there is 

 little doubt that it is Manhattan schist. The mica has evidently been 

 largely altered or absorbed by the igneous rocks, leaving a very quartzose 

 residue ; and it would seem, therefore, that these inclusions may thus en- 



36 Amer. Jour. Sci., (3), XX, 195. 1880. A minute description of a number of inclu- 

 sions is here given. 



