DESCRIPTION OF PLATES. 



Reproduced by the artotype process from microphotographs in polarized light. 

 The enlargement is given under each figure. The eight figures which are de- 

 scribed in the text represent a partial series exhibiting tlie supposed progressive 

 changes in original detrital feldspar grains until complete obliteration of the 

 original characters is attained. 



Figures 1 and 2 represent the earlier stage in undoubted clastic grains. 



Figures 3, 4, 5, and 6 represent an intermediate stage. Figure 6 is the left hand 

 central portion of Figure 6, more highly magnified, in order to show the rami- 

 fication of the clear feldspar in the cloudy feldspar. 



Figure 7 represents the almost completed stage, and 



Figure 8 the albitic type of feldspar in which there is no trace of clastic origin. 



