Granite. 465 



ous that it must have been greater where the granite was produced 

 than where the sienite is now found. For even if we do not 

 suppose the sienite to have resulted from the fusion of stratified 

 rocks, yet the proximity of its materials to these rocks must 

 have greatly reduced the temperature of these materials: and if 

 the stratified rocks were melted to form it, still more certainly 

 would such be the result. Whether the position of sienite in other 

 parts of the world is similar to that in the place under consideration I 

 know not ; nor can I say whether that in the eastern part of Massa- 

 chusetts will throw any light upon these speculations. 



This suggestion as to the ground of difference between sienite and 

 granite, derives some support from the great scarcity of crystalized 

 minerals in the former compared with those in the latter. I can imag- 

 ine no cause for this difference so probable as a more or less perfect 

 fusion of the materials. The history of porphyry leads the mind to 

 the same conclusion. 



These hypothetical views I am aware are new. But I have been 

 led to form them from the facts that ha\e been detailed; and if they 

 are thought by geologists to deserve consideration, I hope that facts 

 derived from other deposits of sienite and granite will be brought to 

 light, to prove their fallacy or correctness. 



18. GRANITE. 



Having included under sienite all those unstratified granitic com- 

 pounds which contain hornblende as a constituent, the definition of 

 granite becomes easy. It is, indeed, the common definition, which 

 makes it to consist of quartz, feldspar and mica. Dr. Macculloch adds 

 hornblende: but it seems to me that this destroys the usual distinction 

 between granite and sienite. Granite may, indeed, contain dissemin- 

 ated crystals of hornblende, as of garnet, pinite, or any other min- 

 eral ; but if the quantity of this hornblende is so great that it must be 

 regarded as a regular constituent of the rock, I do not know why it 

 should not take the name of sienite, unless we should merge all sien- 

 ite in granite : and to this I have no objections. I can conceive, in- 

 deed, how the geological relation of granite with hornblende, may be 

 such to granite without hornblende, that it would be preposterous 

 to attempt to separate them : but I know of no such case in Massa- 

 chusetts. Here sienite occupies, as we have seeen, a constant geolo- 

 gical position in respect to the granite about to be described. 

 59 



