wherey: cavities in zeolite deposits 183 



suggested itself, and the angles, habit, and curvature of faces 

 (due to oscillatory combination) of plaster casts of a few of them 

 were found to be essentially identical with those of glauberite. 5 

 That glauberite has not been considered in this connection before 

 is probably due to the fact that the crystals figured in Dana's 

 System of Mineralogy happen to be all of tabular habit, although, 

 as noted in the text, this species is not infrequently prismatic, 

 owing to the extension of the form s. This form is usually 

 regarded as the unit pryamid, but it may well be questioned 

 whether it might not be made the unit prism. 6 The forms which 

 have been observed on the cavities in the zeolites are c (100), 

 «(334), e(445), s(lll), ro(110), a(100), and e(311); the most 

 important angles are sas' 63°42' (the prismatically developed 

 form), cas 43° 2', CAa' 112°11', sAe 4°55', sa« 6°21', and a'*e 

 31°42', variations of several degrees owing to the oscillatory 

 combination of forms being frequent in these angles, a phenom- 

 enon observed also in many crystals of the mineral. 



The identification of the mineral of these cavities as glauberite, 

 though based primarily on crystallographic data, is confirmed 

 by geological and genetic considerations. At Steinsburg and at 

 Princeton the mineral crystallized in the sediments as a result 

 of concentration of the water in enclosed lakes. Most of the 

 known occurrences of this mineral are in this sort of deposit, and 

 it is always one of the earliest to form. The basalt lava of the 

 First Watchung Mountain, as shown by Dr. Fenner, 7 flowed 

 locally into a similar lake, the waters of which contributed to 

 the formation of the zeolites and other minerals and could 

 readily have furnished the calcium sulphate of the anhydrite 

 and the additional sodium sulphate of the closely associated 

 glauberite. It is noteworthy that glauberite has been observed, 8 



5 Dr. W. T. Schaller of the U. S. Geological Survey has made an extensive 

 series of measurements of the angles of the quartz "cores" found in some of the 

 cavities, and he kindly lent his notes to the writer for comparison; complete 

 agreement with the artificial casts was shown. 



6 In a subsequent paper this new orientation of the mineral will be fully dis- 

 cussed by Dr. Schaller. 



7 Ann. N. Y. Acad. Sci. 20: 93-187. 1910. 



8 Bergeat. Zeit. prakt. Geol. 7: 43. 1899. 



