134 



ANNAL8 NEW YORK ACADEMY OF SCIENCES 



tion of a single quartz crystal, which has been almost completely replaced 

 by datolite. There is little tnrbidity in either quartz or datolite. In 



7i/arf. 



/.j/fite 



*rc /tn / /e 



Fig. 9. Fragments of quartz with prebuite being replaced by apophyllite. 

 Quartz is conventionally stippled to distinguish it from apophyllite. X 35. 

 Slide 138. 



numerous other places, parting planes in the datolite appear to outline 

 former quartz crystals, that is, the replacement of quartz has given rise 



ift/orrx 



CAmitazitc 



Fig. 10. Quartz cut by vein of chabazite and corroded by same on margin. 



X 35. Slide 146. 



to roughly pseudomorphic forms of datolite. In 125, also, pyramidal 

 quartz crystals have been slightly replaced by datolite. 



