rl44 NEW YORK STATE MUSEUM 



For a detailed discussion of the geology of this part of the area, 

 reference must be made to Dr Merrill's paper on the " Crystal- 

 line rocks of southeastern Kew York," published in the 50th 

 annual report of the New York state museum. Reports on 

 Orange and Rockland counties, by Dr Ries and Dr Ktimmel 

 respectively, have also been issued. The Devonian outlier 

 extending in Orange county from near Cornwall to Greenwood 

 lake, has been discussed in detail by Mr N. H. Darton. 



The oldest formation in the area is a series of gneisses of pre- 

 Cambrian age, forming the mass of the Highlands. To the 

 northwest of this range is the great lowland, based on Cambro- 

 Ordovician limestones and shales. A structural basin lying on 

 the northwest flank of the main body of pre-Cambrian rocks, but 

 separated from the Paleozoic lowland in Orange county by a 

 series of small pre-Cambrian outliers, contains Upper Silurian 

 and Devonian formations. East and southeast of the pre-Cam- 

 brian mass, on the western side of the Hudson, is a region in 

 which the sedimentary rocks have been highly metamorphosed, 

 the sandstones, limestones and shales of the normal Cambro- 

 Ordorician appearing here as quartzites, highly crystalline lime- 

 stones, and schists. As a further result of the forces to which 

 they have been subjected the strata, originally laid down in a 

 nearly horizontal position, now form a series of folds, trending 

 generally northeast and southwest, both Paleozoic and pre- 

 Cambrian beds being involved in these folds. South of the pre- 

 Cambrian, to the west of the Hudson river, these altered 

 Paleozoic rocks are almost entirely overlain by the Newark 

 rocks, which cover most of Rockland county. In addition to 

 the formations noted above, which are parts of a normal suc- 

 cession, igneous rocks occur as intrusives of later date. 



SUCCESSION OF THE FORMATIONS 



Pre-Cambrian rocks 



The pre-Cambrian rocks of southeastern New York consist 

 of a series of gneissoid granites and gneisses, locally schistose. 

 In Westchester county the more massive (and in general more 



