ON A BASIC ROCK DERIVED FROM GRANITE. 679 



data are scanty and unreliable. The composition of the rock, 

 shown in IV., is so different from that of the Old Sterling rock, 

 as to raise some doubt of a unity of origin. This is particu- 

 larly true when it is considered that the Caledonia rock, if 

 derived from a granite, has generally lost all trace of its quartz, 

 and yet has suffered less chemical change than has the Old 

 Sterling rock, in which much quartz still remains. This fact 

 might, however, be accounted for by some difference in the 

 solutions causing the alteration, or by a more complete crushing 

 of the granite. The latter explanation is particularly probable, 

 as the granite of the region not uncommonly runs over into very 

 fine granulitic phases. There are, moreover, very pronounced 

 indications of crushing and shearing in the rock of this locality. 

 Some specimens of the rock, however, contain quartz, and in 

 thin sections closely resemble the Old Sterling specimens. 

 Examination of these sections makes it difficult to avoid the 

 conclusion that the Caledonia "serpentine " is also an altered 

 granite. The microscopical evidence in favor of such a conclu- 

 sion is very strong, though not affording, as in the case of the 

 Sterling rock, a complete demonstration. 



From the facts at hand it may be stated that the so-called 

 serpentine of the various mines is derived from different rocks, 

 whose character must be determined in each case. There is 

 nothing to indicate that the original rock was, in any instance, 

 a basic intrusion, but, on the contrary, where it has been found, 

 it is decidedly acid. Moreover, the alteration products are not 

 sufficiently uniform in character to be grouped under a specific 

 name, and, even were this done, the term serpentine, which has 

 always been applied to them, would have to be supplanted by 

 something more in accord with their composition. 



C. H. Smyth, Jr. 

 Hamilton College, 



Clinton, N. Y. 



