130 



port on the Geology of the State, has given us descriptions of 

 the lithologic characters of these rocks which are for the most 

 part comprehensive and accurate ; and this part of the subject 

 may be passed with brief notices here. 



Gea^ite. — The granites are of two distinct kinds, — dis- 

 tinct in origin, but often difficult to distinguish with the eye. 

 They are exotic and endogenous. The exotic or eruptive 

 granite is of most importance. It is usually whitish or gray, 

 — seldom red or greenish, as the Huronian granite frequently 

 is ; and it differs further from the Huronian granite, in that it 

 is always more or less micaceous, and rarely contains any 

 hornblende. 



This variety, especially, is everywhere intimately associated 

 with the gneiss, and it is clearly to be regarded as a part of the 

 great gneissic terrane which has been softened and forced out of 

 its original position. The evidence on this point is of the 

 strongest character.^ In considerable masses of the gneiss, 

 however, the metamorphism has apparently stopped short of 

 actual extravasation, although all traces of bedding are lost. 

 And in still other cases, probably, the gneiss wears a granitoid 

 aspect where it has experienced no special alteration, having 

 always been coarse-grained and massive. As may be readily 

 conceived, it is often a matter of extreme difficulty to distin- 

 guish these granitoid gneisses or indigenous granites from the 

 truly eruptive rock. The exotic granite passes insensibly into 



1 It is a remarkable fact, and one strongly suggestive of the derivation of the exotic 

 rocks, in those cases, from the stratified rocks which they penetrate, that, although 

 the Huronian and Montalban granites are strikingly contrasted in their mineralogical 

 characters, each presents a substantial agreement in this respect with the indigenous 

 terrane which it intersects, or with which it is most intimately associated. To appre- 

 ciate the force of this statement, and to realize that the granites have originated in, 

 and hence are peculiar to, and, in the fullest sense of the words, essentially a part of, 

 the great formations "with which they are respectively connected, it would seem to be 

 only necessary to compare (1) the red, brown, greenish, and gray Huronian granites, 

 which consist essentially of orthoclase and quartz, with the similarly colored and con- 

 stituted stratified petrosilex of that formation; and (2) the light-colored, almost 

 white, micaceous Montalban granite with the intersected gneiss, from which it is 

 usually distinguishable only by the absence of stratification. 



