LITHOLOGY. 1 89 



though of great geological interest, may be wholly unrecognizable in the 

 lithological study of specimens. All the features referred to are very 

 often found in our state. There are beds of granite which are conforma- 

 ble with associated stratified rocks. There are granites filling well 

 defined dykes. There are granites which, so far as can be seen, are 

 entirely void of structural relationships. There are granites which are 

 mixed with other rocks, or which hold huge fragments of other rocks 

 enclosed in their masses. All these features are often repeated; and 

 when one wonders at their diversity, he has but to think of those tre- 

 mendous movements which have taken place in the crust of the earth, 

 and that any plastic materials which were influenced by these move- 

 ments would take the forms and relationships to other rocks which local 

 circumstances determined. 



Dr. Hunt, who has made a careful study of the granites of this part of 

 the world, has divided them into three classes. The first class embraces 

 the granites which are in place among the strata, and which he calls 

 indigenous granites ; the second class embraces the intrusive granites, 

 which are called exotic ; and the third embraces granitic veinstones, 

 which are called endogenous. The members of the last class are dis- 

 tinct in origin, and hence in lithological characters. The rocks of the 

 exotic class, however, show just the same evidences of having solidified 

 under pressure as do those in place. It is not claimed that they result 

 from eruptions that reached the free surface where the pressure would 

 be removed, but they entered cracks in overlying strata, and solidified 

 like the others in the depths of the earth. Hence the members of the 

 first two classes cannot be expected to be lithologically distinct. 



The minerals of which the rocks of this group are composed are 

 quartz, orthoclase, and plagioclase, of which, in variable proportion, the 

 bulk of the rock is always composed; and muscovite, biotite, hornblende, 

 augite, chlorite, tourmaline, graphite, and hematite, one or more of which 

 may be present as characterizing accessories ; and beside these, a variety 

 of minerals, such as apatite, rutile, zircon, microcline, &c., are micro- 

 scopically detected, and which are of interest, though they form no pro- 

 portion of the bulk of the rock. 



Authorities differ in sub-dividing this group. Some, considering quartz 

 and feldspar as the essential constituents, sub-divide the rocks into gran- 



