348 GEOLOGICAL APPEARANCES 



the main rocks, it may be opposed with peculiar force by the. 

 last argument. The formation of the main rocks of sienite 

 cannot be explained by secretion ; and the improbability that 

 two separate processes should have agreed in producing in 

 contiguous spots a substance so rare elsewhere, as this sienite, 

 is materially increased, when those two processes are supposed 

 to have differed in kind. 



120.. From the veins, which consist of a sienite similar to 

 that of the main rocks, it is easy to extend the argument to al- 

 most all those veins, which consist of various aggregates of fel- 

 spar and quartz, or felspar and hornblende, with a little mica 

 in one or two places, and those whieh contain felspar only. 

 These present a great diversity in their ingredients, and in the 

 size of the grains; but their continuity with the veins of sie- 

 nite, and the gradation of the substances composing them into 

 the sienite, were traced in many instances, even where the 

 veins were most minute and obscure, and their ramifications 

 most complex. These circumstances furnish sufficient grounds 

 for referring their origin to the same fluid mass. Above the 

 bridge, where the specimens were procured by a blast, we 

 found many of the most minute and complex veins of this 

 kind to graduate into veins of sienite, which again were joined 

 to the main rock of sienite, and grew larger as they approach- 

 ed it ; while we observed that in a stratified rock, of precisely 

 similar characters, a little farther to the eastward, there were 

 no such veins, or scarcely any. (Parag. 90, 93.) This, 

 while it seems to exclude every explanation of those veins 

 from circumstances attending the formation of the strata, 

 points strongly to the once fluid substance of the main rock of 

 sienite for their undoubted origin *.. 



121. We 



* See no.te.B at the end of the papa'. 



