88 



Cincinnati Society of Natural History. 



minerals to slide along their borders. The crystals would 

 yield at these points which are lines of weakness in the rocks, 

 since the force of adhesion between contiguous minerals 

 would be more easily overcome than the force of cohesion 

 within the crystal itself. In a number of cases, as cited in 

 this section, the force was great enough to also overcome this 

 property of cohesion. 



Chemical Composition of the Rowlandville 



Granite. 



For the chemical investigation of the Rowlandville granite 

 type the specimen was selected which showed, under the 

 microscope, the least alteration. This was collected in the 

 railroad cutting at the edge of the town of Rowlandville. It 

 is a dark-colored granitite, containing somewhat more than 

 the usual proportion of biotite. It contains an abundance of 

 idiomorphic plagioclase crystals, with zonal arrangement of 

 epidote, considerable unstriated feldspar which also contains 

 epidote, and abundant quartz. The needles above described 

 are present both in the biotite and quartz. A complete 

 chemical analysis of this rock was made by Dr. W. F. Hille- 

 bra'nd, of the United States Geological Survey, with the fol- 

 lowing result : 



Si 2M ^, v . , . . . • ■ • 66.68 



Ti 2 , 50 



Al, O,, 14.93 



Fe., O,, 1.58 



Fe O 3- 2 3 



• Mn O, 10 



CaO, 489 



Sr O, Trace 



Ba O, c8 



Mg O, ' 2.19 



K 2 O, 2.05 



Na 2 O, 2.65 



Li 2 O, Trace 



H, O, below no° C, .' 16 



H 2 O, above no° C, T.09 



P, 5 10 



Total, 100.32 



