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, 1s 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 
