So 



Cincinnati Society of Natural History. 



as a secondary mineral, resulting from the alteration of feld- 

 spar and bleaching of biotite, it also occurs, in a few cases 

 at least, as a primary constituent, for it is bordered, inter- 

 grown, and even completely enclosed in fresh, strongly 

 pleochroic biotite, and it has bent and broken cleavage 

 lamellae. This mineral contains inclusions similar to those 

 found in the biotite, such as epidote and the small needles. 



Quartz, in the form of a 

 more or less coarse mosaic, 

 occurs in large amounts in 

 the Rowlandville granite. 

 In a number of cases a con- 

 siderable quartz area was 

 seen to have once belonged 

 to a single individual, from 

 the regular grouping of cer- 

 tain abundant hair-like in- 

 clusions toward the center. 

 Between crossed nichols' 

 such an area is now seen to 



Fig. 1.— Quartz Mosaic, with hair-like iuclu- ^ e a mOSaic of interlocking 



sions, from Rowlandville granite. grains, as is diagramatically 



x 80 



shown in Fig. i. Each hair- 

 like inclusion is broken at the junction of two quartz grains, 

 and we may infer from this, that the quartz has been crushed 

 subsequent to its original solidification. 



ORIGINAL ACCESSORY COMPONENTS. 



All of these Rowlandville granites possess a varied original 

 mineralogical composition through a large number of acces- 

 sory constituents. The most abundant of these is allanite, 

 which is found in nearly every granite specimen, varying in 

 size from minute grains to crystals 2 mm. in length, with zonal 

 structure and strongly pleochroic. Since, however, this min- 

 eral is better developed in the Port Deposit granite, its physi- 

 cal and optical properties will be more fully described in the 

 next chapter. 



Zircon is a widely-distributed constituent, and occurs in 

 most of the sections as small, stout prisms, doubly terminated. 



