THE GEOLOGY OF MOUNT KEARSARGE 405 



The specific gravity of the granite is 2.624, and its composi- 

 tion is shown in the following analysis:' 



SiOj ------ 73.01 



AI2O3 ----- 13.73 



FCaOs ------ 0.44 



FeO ----- 1.48 



MnO - - - - - - 0.09 



CaO - - - - - 0.94 



MgO ------ o.oi 



K2O - - - . . 5.62 



NajO ------ 3.50 



Loss at iio"C - - - - .05 



Loss over blast - - - - .18 



99.05 



The weathering of this granite is very characteristic. Every 

 bowlder in the fields has partly or entirely crumbled to a barren 

 ring of gravelly debris. This debris consists of loose, angular^ 

 rusty particles varying in size from those an inch through down 

 to fine powder. The particles consist, as far as can be seen, of 

 orthoclase and quartz. The former, during the disintegration, 

 loses its luster and bright flesh-red color, and assumes a dirty 

 rusty color ; it does not, however, become covered with a fine 

 powdery coating of kaolin, but is divided into little cleavage 

 blocks by many cracks along the cleavage planes. The angular 

 quartz grains are thrown out by the breaking of the feldspar, and 

 the anhedra and quartz crystals may be found among the par- 

 ticles of the crumbling rock. 



The mica is generally decayed, and has changed from a black 

 to a brownish, bronzy, or brassy color. Secondary epidote is 

 frequently seen with the decaying biotite. The triclinic feldspar 

 is rarely seen in the disintegrated particles of this granite. 



The analysis of a fair sample of some of the coarser of these 

 particles afforded : 



'Other determinations were not made. The methods given in Bulletins 148 and 

 176, U. S. Geo/. Surv., were closely followed. 



