164 GEOLOGY AND MINERALOGY OF NEWBURY. 



1. Granite. It will be noticed by recent students of 

 geology that several changes have taken place in the classi- 

 fication of our rocks. The old name syenite has given 

 place to that of hornblendic granite, as being more specific. 

 The term granite is now used to cover many varieties of 

 rock, all crystalline, ranging from distinct diorite on the 

 one hand to felsite on the other. The specific names of 

 these varieties are determined by the presence or absence, 

 and the greater or less quantity, of certain constituent min- 

 erals, mainly hornblende, in the rock. I have always 

 maintained, and this is the view now generally accepted, 

 that there are no absolute distinctions between rocks. 

 There are varieties almost infinite, but no absolute species. 

 It is possible to arrange a continuous scale of specimens 

 covering the whole series. 



It is necessary to have specific names for strongly 

 marked rocks, though these resolve themselves into varie- 

 ties that shade off again into other species. It requires 

 long familiarity with, and close study of, all classes of rocks 

 to be able to determine these specific distinctions. When 

 even the professors and geological authors differ so much 

 in their classifications, amateurs need not feel cast down 

 by an occasional mistake. 



In Newbury a fine hornblendic granite is developed in 

 two bands or ridges running east and west, enclosed by 

 diorites, and broader and coarser at the eastern than at 

 the western end. 



The serpentinic limestone is associated with this granite, 

 which led Dr. T. Sterry Hunt to call it Laurentian ; but 

 the whole formation is pronounced by Mr. Crosby to be 

 Huronian. 



2. Felsite. This term is now used to cover many 

 varieties of rock, some of which were formerly called 

 porphyry, metamorphic slate, hornstone, etc. 



