194 NEW YORK STATE MUSEUM 



Westchester, Putnam and Dutchess counties, but also occur in 

 Orange county as a continuation of the northern New Jersey belts. 

 Those of a thoroughly crystalline character are associated with 

 schists, quartzites and thin-bedded gneisses, forming a series of 

 interfolded metamorphosed sediments that bear some resemblance 

 in certain aspects to the Grenville series .of the Adirondacks. Their 

 stratigraphic position is doubtful ; it would appear that they may 

 represent more than one period of formation, as indicated by the 

 varying degree of metamorphism which they have undergone. 



In Westchester county the limestone is coarsely crystalline, white, 

 and usually carries magnesia in proportions characteristic of dolo- 

 mites, though in the very northern part of the county there are 

 limestones with low magnesia. The name " Inwood " was first 

 applied to the limestones by F. J. H. Merrill, who later advocated 

 the view of the general equivalence of the limestones in this section 

 with those of western New England and withdrew that name in 

 favor of the prior term " Stockbridge " limestone. Merrill and 

 other geologists have regarded the Westchester county limestones 

 as a southerly extension of the belts that are found north of the 

 Highlands where they are much less metamorphosed and are known 

 to be of Cambro-Ordovicic age. 



More recently Berkey has indicated the possibility of the ex- 

 istence of two main series of limestones. The Westchester county 

 representatives, accompanied by the Lowerre quartzite and Man- 

 hattan schist, show no marked unconformity with the underlying 

 gneisses, and are considered as Precambric. The second assemblage 

 includes the less changed types of white and blue limestones, de- 

 veloped mainly to the north of the Highlands, which have been 

 known as the Wappinger limestone and which are associated with 

 the Poughquag quartzite and the Hudson River slates. These 

 show a marked unconformity in contact with the gneiss formation. 

 Small bands and lenses of impure limestone occur within the High- 

 lands gneisses, and are probably the oldest of all, that is of Gren- 

 ville age. The latter have little economic importance. 



The crystalline limestones of southeastern New York are pre- 

 vailingly high in magnesia, though there are some localities where 

 they carry under 5 per cent. In the developed marble quarries the 

 stone is usually a true dolomite. The proportion of lime carbonate 

 ranges from 55 per cent as a lower limit to about 70 per cent, while 

 the magnesium carbonate amounts to from 30 to 45 per cent. The 

 siliceous impurities are usually low, not over 2 or 3 per cent of the 



