270 IRVING. 



Garnet i^Mdaiiiie). — In the phonolite from the summit of 

 Ragged Top Mountain, masses of this mineral can be observed. 

 It is dark brown, with irregular fracture and high rehef, and 

 between crossed nicols shows faint double refraction. It is sur- 

 rounded by a dark mass consisting of interlocking crystals of 

 segirine and aegirine-augite mingled with magnetite grains and 

 an undetermined decomposition product. 



Lciicitc (?). — In 1897 a series of rocks from the Black Hills 

 was sent to Professor Kemp by Professor F. C. Smith, of the 

 Rapid City School of Mines, and determinations were made by 

 Mr. D. H. Newland in the laboratory of Columbia University. 

 Among these rocks were a set which were determined as leuci- 

 tophyres and leucite-phonolites, and were described as such by 

 Professor Smith in his paper on the " Potsdam Gold Ores of 

 South Dakota."^ It was also on the basis of these determina- 

 tions that the statement was made by Professor Kemp, in a paper 

 on the leucite hills of Wyoming, that leucite rocks were abun- 

 dant in the Black Hills. Since then further investigation seems 

 to show that this mineral may prove to be one of the sodalite 

 group, or at least that its determination as leucite is somewhat 

 questionable. 



The most perfect instance of a rock of this kind is that oc- 

 curring in a thick sheet at the mouth of Anne Creek, where it 

 enters Spearfish Cafion. A similar rock was found in a shaft 

 northwest of Carbonate. The other leucite rocks occur in a 

 mass on the divide to the south of Ragged Top, on Green 

 Mountain, and on the edge of the limestone bluff opposite Lit- 

 tle Spearfish Falls. In addition to these, the writer has found 

 a great many occurrences showing the same isotropic mineral 

 in greater or less abundance. 



In microscopic appearance, the rocks containing this mineral 

 do not differ from those of the phonolite series, but show the 

 same variations from a dense texture and dark green color to 

 lighter gray and more coarse-grained rocks. The rock from 

 Annie Creek shows the typical dense texture and green color 

 of a tinguaite. The phenocrysts are sm.all and inconspicuous, 



1 Trans. Am. Inst. Mining Engineers, Vol. XX\'II, p. 41 1, July, 1897. 



