Plate 23 



Photomicrograph showing structure of the reeding quality of "blue- 

 stone." Magnification 30 diameters. Taken to show tendency to paral- 

 lelism of elongate grains. 



Photomicrograph of best grade coarse-grained bluestone. Taken to 

 show a quality in which the granular character is still well preserved. 

 The clear grains are quartz, the others are chiefly feldspars somewhat 

 modified. The close interlocking and the development of fibrous or 

 frayed structure and the bending or wrapping of some constituents are 

 secondary effects. 



