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 the 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 8, 4, 5, and 6 represent an intermediate stage. Figure 6 is the left hand 
central portion of Figure 5, 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. 
