182 wherry: cavities in zeolite deposits 



early stage, became surrounded by quartz, prehnite, or zeolites, 

 and at some subsequent time dissolved away. Replacement by 

 quartz also took place at various stages in the history of these 

 crystals, so that the cavities sometimes show lamellae where 

 the quartz entered along cleavage planes, and in other cases 

 have been completely filled by quartz, occasionally yielding 

 a removable core. Two types of crystals are represented, one 

 rectangular in outline, thick to thin tabular in habit, and evi- 

 dently orthorhombic, the other lozenge or " diamond "-shaped 

 in cross section, prismatic in habit, and monoclinic in symmetry. 



Babingtonite was suggested by Dr. C. N. Fenner 2 as the original 

 mineral of the rectangular cavities, and possibly of the lozenge 

 shaped ones as well, while Mr. F. I. Allen 3 has shown that 

 anhydrite was the original occupant of the former in many cases. 

 Reasons are here presented for believing the mineral of the lozenge 

 shaped cavities to have been glauberite, Na 2 Ca(S0 4 )2- 



In connection with studies of the Triassic rocks of the eastern 

 United States the writer has long been interested in the angular 

 cavities occasionally found in the shales, and while examining 

 specimens of these from one mile south of Steinsburg, Bucks 

 County, Pennsylvania, obtained a clue to the nature of the 

 original mineral. Plaster casts of the well-preserved cavities 

 in this shale were prepared, and found to have the angles, habit, 

 and type of oscillatory combination of faces, resulting in stria- 

 tions and rounding of faces, characteristic of glauberite. No 

 trace of the original mineral is here preserved; but in another 

 occurrence, described by Mr. A. C. Hawkins, 4 the crystallization 

 of the mineral in the muds in downward-radiating groups of 

 long slender monoclinic (or triclinic) prisms and the filling of 

 its cavities by secondary analcite and calcite (which contain 

 sodium and calcium respectively) indicate that the original 

 mineral here also was probably glauberite. 



Comparison of the lozenge-shaped, prismatic cavities in the 

 First Watchung Mountain zeolites with glauberite thereupon 



2 Journ. Wash. Acad. Sci. 4: 552-558, 598-605. 1914. 



3 Amer. Journ. Sci. 39: 134. 1915. 



4 Ann. N. Y. Acad. Sci. 23: 163. 1914. 



