372 



Scientific Geology. 



that place drusy quartz occurs, which is extremely beautiful. In the 

 serpentine of Newfane, Vt. a similar drusy quartz has been found 

 abundantly. Here also occurs chrysoprase ; and sometimes the 

 small crystals of quartz occupying the cavities of the rock have the 

 color of the chrysoprase. At the same place general Martin Field 

 has discovered pimelite. 



Theoretical Considerations. 



The preceding description will show that the serpentine of Massa- 

 chusetts corresponds essentially, as to position and character, with 

 those serpentines in Europe that are connected with the oldest rocks. 

 But I am not aware that any statements which I have made, will 

 throw additional light on the obscure subject of its origin. From the 

 statement of Dr. Macculloch* and De la Beche,f as to the connection 

 between serpentine, trap, and limestone, one would be led to infer that 

 the first mentioned rock might have resulted from a mixture of the 

 trap and limestone. But the serpentine of Massachusetts does not 

 favor such an idea. The precious serpentine of Newbury prob- 

 ably lies between the sienite or greenstone and the limestone ; 

 and such is its position in the cases described by these writers. The 

 Westfield serpentine also contains a mixture of carbonate of lime, 

 and in one or two other beds it may be found in small quantity. But 

 in general our serpentines are entirely separated from limestone; and 

 in respect to the gneiss east of Connecticut river, containing one or 

 two of these beds, the whole extensive range does not to my knowl- 

 edge embrace a single bed of limestone. But in all cases, (except 

 perhaps that at Newport,) our serpentines are associated with talc, 

 either pure and foliated, or as steatite, or chlorite slate, or talc and 

 quartz. The two minerals, (talc and serpentine,) are intimately 

 blended together and pass into one another by insensible gradations. 

 And in all the cases described by the writers above referred to, talc 

 was present. Is it not natural then to suspect that serpentine is talc, 

 or talc serpentine, altered by heat 1 And since the talc is schistose and 

 the serpentine massive, the latter must have been produced from the 

 former. In some cases it is easy to imagine that the internal heat 

 might have been powerful enough to produce perfectly fused, and of 

 course compact serpentine, protruding among other rocks in the form 



* Edinburgh Journal of Science, Vol. i. p. 1. 

 t Manual of Geology, p. 497, 2d edition. 



