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NEW YOEK STATE MUSEUM 



The more rapid decomposition of the micas makes those varieties 

 in which they occur in large flakes or aggregations more liable 

 to decay. The condition of the feldspar also is often such as to 

 influence the durability. When kaolinized in part, it is an 

 element of weakness rather than of strength. The presence of 

 the easily decomposable varieties of pyrite is not only prejudicial 

 to strength and durability but also to the beauty of the stone as 

 soon as it begins to decay. 



The term " granite" as used among builders and architects 

 is not restricted to rock species of this name in geologic 

 nomenclature, but includes what are known as gneisses (foli- 

 ated and bedded granites), diorites, gabbro and other crystal- 

 line rocks whose uses are the same. In fact, the similar adapta- 

 bility and use have brought the latter species into the class of 

 granites. For example, the Au Sable granite of Essex county is 

 a norite. The term is applied in some cases to the diabases or 

 trap-rocks, as the " granite quarries " of Staten Island. 



Another massive crystalline rock which is used in building is 

 norite, consisting of labradorite and hypersthene, with some 

 brown mica. It is a common rock in the Adirondack region, and 

 is known commercially as a granite. 



The massive crystalline rocks are of common occurrence in 

 New York, but not in outcrops over extensive areas, excepting in 

 the Adirondack region and in the Highlands of the Hudson. 

 The schistose crystalline rocks are developed extensively in the 

 Highlands of the Hudson and on the borders of the Adiron- 

 dack region. On New York island and within the city limits 

 the gneissic rocks have been quarried at many points. In 

 Westchester county there are belts of gneiss and mica schist, 

 in which quarries have been opened near Hastings; near 

 Hartsdale, east of Yonkers; at Kensico; at Tarry town and 

 at Ganung's, west of Croton Falls. In Putnam county there 

 are quarries of granite near Peekskill and near Cold Spring. 

 West of the river there are quarries on Iona island ; at West 

 Point; near Suff era's; at Ramapo; on Mount Eve, near Florida, 

 and on Storm King mountain, near Cornwall. The outcrops of 

 the gneissoid and granitoid rocks are so numerous in the belt of 

 the Hudson Highlands that quarries can be opened at many 

 points. The supply of stone is inexhaustible. On the Hudson 



