CHAPTER XIV 

 STONE OF THE KENSICO QUARRIES 



The following quarries in the immediate vicinity of Kensico res- 

 ervoir have been studied in the field: 



(i) '' Smith quarry," which is less than a thousand feet east of 

 the southern end of the present reservoir; (2) '' City quarry/' which 

 is on the immediate eastern margin of the reservoir on the east side ; 

 (3) " Garden quarry/' which is a new location about 500 feet from 

 the eastern margin about midway; (4) " Outlet quarry/' 1500 feet 

 east of the northern extremity of the present reservoir; (5) " Ferris 

 quarries " 1000 feet and (6) " Dinnan quarry " 30cmd feet farther 

 north. 



In addition to the field observations a detailed microscopic study 

 was made on specimens of the rock taken from the Garden, Ferris 

 and Dinnan quarries. 



The question at issue is the choice of a rock for the facing and 

 finish of the new Kensico dam. In view of the use to be made of 

 the rock, extreme strength is of only secondary importance. But the 

 questions of abundance, distribution, durability, purity, agreeable 

 appearance and working quality are vital. 



Types of rocks 



All of the quarries occur in the broad belt of Precambric gneisses 

 that forms the eastern margin of the reservoir extending northward 

 and soutliward for many miles. The formation as a whole is vtry 

 complex. But the basis of it is a black and white banded rock 

 chiefly a metamorphosed sediment, know^n as the Fordham gneiss 

 in southeastern New York. In it are intrusions of igneous rocks 

 of many varieties and most complicated structure — dykes, bosses, 

 veinlets, stringers etc., sometimes in such abundance as to wholly 

 obscure the original type. The most abundant of these are, (a) a 

 rather light colored quite acid rock that is essentially a granite in 

 composition, but has a sufficiently foliate structure to be classed as 

 a gneiss and is the same as the "' Yonkers gneiss " occurring farther 

 south, and (&) a dark rock containing much hornblende and biotite 

 which is in some cases essentially a diorite in composition, but has a 

 marked tendency to schistose structure. The former (a) may be 

 called a granite gneiss and the more massive representatives of the 

 latter (5) may be classed as a dioritic gneiss. In both cases at 

 7 19.^ 



