CRYSTALLINE STRUCTURES OF ROCKS. 191 



know that it exists ; we are ignorant alike of the laws 

 of both. But that they have a real connexion, is 

 proved by the phenomena above recited respecting 

 the smaller spheroidal structures. In these, it is abso- 

 lutely impossible to define the point at which the one 

 ceases and the other commences. The radiated cry- 

 stalline spherule passes into one consisting of solid 

 unradiated concentric crusts ; and that again, in a 

 manner equally gradual, into a solid sphere without 

 any internal structure. 



I know not, that at present, any further light can 

 be thrown on this obscure subject. As far as relates 

 to the magnitude of some of the masses considered as 

 concretionary, there is no cause for objections. We 

 can even see no reason why nature might not have 

 produced a crystal of mountainous bulk, provided the 

 requisite circumstances were present. The polar ten- 

 dency of crystallization is often prolonged through 

 various obstacles, as is daily seen in minerals : it may 

 be protracted indefinitely along the atoms of a com- 

 pound mass, as is evinced by the granite vein in 

 Coll elsewhere described ; (Western Islands.) The 

 tendency to form certain concretions may equally be 

 unlimited ; and thus it needs excite no surprise, if 

 even the granitic laminse of the Alps, which have 

 been supposed the products of an extensive but dis- 

 turbed stratification, have been produced by a con- 

 cretionary arrangement analogous to crystallization. 



