Hornblende Slate. 378 



of veins ; while at other times the fusion was only partial, not suffi- 

 cient to destroy entirely the stratification. The great similarity in 

 the chemical composition of serpentine and talc also favors the idea 

 that they had a common origin. Both are composed essentially of 

 silex and magnesia, with a considerable proportion of water. What 

 the original rock could have been, which, with one degree of heat, or 

 with heat applied under certain circumstances, could have become 

 converted into talc, and with another degree of heat, or with heat ap- 

 plied under different circumstances, could have produced serpentine; 

 I am at a loss to imagine ; though we do find talcose rocks among 

 some of the older of those that are fragmentary. But I make these 

 observations with little expectation that they will stand the test of ob- 

 servation. It may be found that serpentine has been produced from 

 various rocks, which contained the necessary ingredients. But that 

 heat has been employed in its production, cannot it seems to me, be 

 reasonably doubted. 



13. HORNBLENDE SLATE. 



I use this name as a translation of Dr. Macculloch's Hornblende 

 Schist; and I include under it the same varieties of rocks. These 

 varieties are such as other geologists have described under the names 

 of hornblende rock, hornblende schist, primitive greenstone, and 

 greenstone slate ; all of which, I believe, occur in Massachusetts. In 

 reading Dr. Macculloch's masterly description of the primary rocks 

 of Scotland, I can hardly conceive that he is not describing those of 

 New England; so perfect is the correspondence. Hence I have fol- 

 lowed that geologist in describing most of the primary rocks ; though 

 I reject some of his distinctions. But upon the whole, I know of no 

 geological writer who will compare with him in treating of the 

 older rocks. I can by no means say the same in respect to his 

 account of the newer rocks. For he obviously endeavors to depreci- 

 ate the value of an accurate knowledge of organic remains found in 

 the secondary and tertiary rocks ; and it is but too evident that the 

 reason is, that he himself can make no pretentions to distinction in 

 this department. As to Dr. Macculloch's views of geological theo- 

 ries also, in his last work, " A System of Geology," whatever opinion 

 may be entertained of their correctness as a whole, I think no one 

 who carefully examines them, will hesitate to acknowledge them, 

 every thing considered, as remarkably profound, ingenious, and ju- 



