460 Scientific Geology. 



a A d, a- a 



Veins in Sienite : Whately. 



It is easy to conceive how the detached portions of these two gran- 

 ite veins might be brought into alignment, (to continue the allusion 

 above made to military manoeuvres,) but how they could have been 

 thrown into their present position, except when the rock was in a 

 fluid state, I am unable to conceive. And yet there must have been 

 consistence enough in the veins to prevent their being diffused 

 through the sienite. Does not this example lend some plausibility to 

 the suggestion that has been made, relative to the protrusion of veins 

 while yet the rock was in a partially fluid state ? Or must we, in or- 

 der to explain such a case as the present, suppose a second fusion of 

 the rock ? 



Geological Position of Sienite. 



I am not aware that any of the sienite of Massachusets can be prop- 

 erly called an overlying rock : that is, I have found no example 

 where it lies above other rocks. On one side it usually passes by in- 

 sensible gradations into granite, and on the other into greenstone or 

 porphyry : Or when these rocks are wanting, some of the stratified 

 rocks, such as hornblende slate, graywacke, or new red sandstone, 

 repose upon it. At least this is the impression I have received from 

 all the examinations which I have made of our sienite ; although I 

 cannot refer to particular spots where these various rocks are brought 

 into the relations that have been described. The low level at which 

 our sienite is placed, has caused it to be very much covered with di- 

 luvium, so as to hide its junction with other rocks. Yet in all cases 

 where this rock occurs, we find it between the oldest granite and 

 greenstone, or the earlier stratified rocks. Hence I infer that a por- 

 tion of the materials of which granite is composed, under certain cir- 

 cumstances were converted into sienite, and that these circumstances 

 existed generally in that portion of the melted granite nearest the 



