88 NEW YORK STATE MUSEUM 



stone is fine in grain and shows often a bluish color, but is still 

 prevailingly dolomitic. 



The later investigations which have been carried out chiefly by 

 Berkey indicate the possibility of the existence of two series of 

 limestones in the region, one of which belongs to the coarser 

 crystalline type as represented by the Westchester county rock. 

 This is accompanied by strongly metamorphosed sandstones and 

 argillaceous sediments known as the Lowerre quartzite and the 

 Manhattan schist, the whole series showing no marked uncon- 

 formity with the underlying gneisses. The age of the series, ac- 

 cording to Berkey, is Precambric and may be called Grenville. 

 The second assemblage of sediments includes the less metamor- 

 phosed representatives that are developed mainly to the north of 

 the Highlands and include the Wappinger limestone, the Pough- 

 quag quartzite and the Hudson River slates of Cambric and Or- 

 dovicic age. Strong unconformity marks their contact with the 

 underlying gneiss. 



The limestones throughout the area are prevailingly magnesian, 

 though they include bands and lenses that are characterized by 

 low magnesia. In most of the developed marble quarries the 

 stone approaches the composition of dolomite with 30 per cent 

 or more of magnesium carbonate. The lime carbonate varies 

 between the lower limit of 55 per cent found in the true dolomite to 

 70 per cent or a little more. The siliceous impurities are usually 

 low, not over 2 or 3 per cent in the marbles. They are due to 

 inclusions of quartz, mica, tremolite, diopside, and more rarely 

 tourmaline. Pyrite is usually present in small amount. 



The marble in this section is found in the more massive heavily 

 bedded parts of the formation, such as are uniform in texture 

 and nearly free of admixture with" silicates. It is predominately 

 white, either uniformly white throughout, or white clouded or 

 banded with blue. It has been mainly used for building stone 

 and both for exterior and interior work. There are numerous 

 examples of it among the larger structures of New York City, 

 especially those erected twenty or more years ago, as at that time 

 it enjoyed greater favor among architects than any other native 

 marble. Of recent years fashion or the exigencies of engineering 

 technic in connection with the very large structures have brought 

 about a change in favor of granite, limestone and terra cotta. 



In durability, the marble from the different localities no doubt 

 varies, and the ease with which some of the stone has weathered 



