514 



Scientific Geology, 



was protruded in a melted state through the slate, and therefore lends 

 some support to that theory. 



Along the western border of the Connecticut valley,the lower beds 

 of new red sandstone in some places have in part lost their red color so 

 as to become spotted. In the adit, for example, at the Southampton 

 lead mine the rock has become gray throughout. (No. 167.) Here 

 we know that a large mass of granite exists within a few feet of the 

 sandstone. Now I have shown under greenstone, that just such a 

 change of color results in this same rock, from a contact with green- 

 stone: and scarcely no one now doubts that the heat of the green- 

 stone was the cause. Why then should it be doubted in the case of 

 granite ? 



5. I infer the igneous origin of granite from its crystalline struc- 

 ture, and the numerous crystalizations of other substances that have 

 taken place in it. 



These same facts I am aware have been adduced to prove the 

 aqueous origin of gianite : for since the products of volcanoes are 

 rarely crystalline, and many splendid crystalizations have taken place 

 from solution in water, it has been thought most reasonable to sup- 

 pose such was the origin of granite. But when has the chemist 

 been able from aqueous solution to obtain a solid crystalline mass of 

 three or four distinct substances at the same time ? I believe 

 never. They always crystalize in succession. And the difficulty 

 is increased when we take into the account the numerous simple min- 

 erals that are found crystalized and enveloped in the granite; each 

 of the substances appearing as if they struggled with one another for 

 a place at the moment of deposition. 



But on the other hand, if the fused materials of which glass is 

 composed, or melted basalt, or lava.be slowly cooled, they will separ- 

 ate into distinct compounds, as has been done in the case of gran- 

 ite. If, however, they be cooled suddenly, a uniform rock, or even 

 a glass will be the result. Does not this fact lead to the probable 

 conclusion, that the degree of crystalization in any rock depends 

 upon the time employed in its refrigeration. Perhaps, however, oth- 

 er circumstances are concerned in causing such a difference in struc- 

 ture as we find between basalt and granite. 



This fifth argument was not adduced to prove the igneous origin of 

 greenstone, because the crystalline structure of that rock is so imper- 

 fect compared with that of granite. Some of the other arguments are 



