36 



west. So far as my observation extends, the hornblendic material 

 of the stratified granite is never distinctly crystalline, but always 

 presents the slaty or chlorite appearance already noticed (ante, 

 p. 28) as frequently characterizing the hornblende of our Huro- 

 nian granites. This incipient or bastard hornblende, although 

 characteristic of the stratified granites, is not peculiar to them. 

 The above are all the instances of any importance that have 

 come under my notice, of the occurrence of stratification, 

 or a structure resembling stratification, in the granites of this 

 formation. Many examples of well-marked bedding have prob- 

 ably escaped observation ; and there can be little doubt that 

 the granites in some cases really possess a gneissic structure 

 where the rock is too coarse and massive to enable the eye to 

 detect it. Yet I do not hesitate to assert that such phenomena 

 must, wherever occurring, be very local ; for it can be proved 

 beyond a doubt that the Huronian granites of this region are 

 mainly exotic. We have seldom far to look to find, in the form 

 of enclosed, angular fragments of clearly-stratified rocks, evi- 

 dence of their extravasation ; and near the boundaries of the 

 granites we often observe them cutting the adjoining rocks, es- 

 pecially if these are stratified, in a manner incompatible with 

 any theory that would regard them, in their present condition, 

 as chiefly indigenous. It is not meant that the extravasation 

 has been universal : it may not have been even general, but 

 certainly a sufficient amount of the granite bears evidence of a 

 foreign birth to warrant the belief that the greater part of this 

 rock has at least been fluent. Prof. N. S. Shaler, in 1869, 1 

 announced the discovery, in the Quincy granite, of structure 

 lines, which he regarded as traces of stratification ; and he was 

 led, in consequence, to suggest the original sedimentary condi- 

 tion of all the granite of that range. The evidence of bed- 

 ding here is certainly much less clear and unequivocal than 

 in the instances cited above ; and although believing with Prof. 

 Shaler, and also with Mr. T. T. Bouve, that all these granites 



i Proc. Bost. Soc. Nat. Hist., xm., 173. 



