RECORDS 481 



work of solution which has been accompHshed is likewise found 

 in the decaying vegetation. The origin of the sulphuric acid 

 required to produce these enormous quantities of gypsum 

 crystals, which have fallen so abundantly as to fill up certain 

 avenues, is still problematic. Only one other mineral is found — 

 flocculent crystals of magnesium sulphate, pendant from the 

 ceiling of two or three small rooms. There are no calcite or 

 quartz crystals. 



The paper was illustrated by lantern slides, showing the pe- 

 culiarities of the stalactite and gypsum formations. 



Professor Kemp in discussion, suggested that the small per- 

 centage of sulphur present in the limestones themselv^es might, 

 after solution of the latter, aggregate sufficient sulphur to afford 

 gypsum along the crevices. Dr. Julien and Professor Steven- 

 son each cited cases in the Caribbean and Bermuda Islands 

 where the amount of vegetation now or formerly growing on 

 the surface was insufficient to accomplish the solution required 

 for the great caves which exist in the coral limestones, both of 

 Tertiary and recent growth in the islands. 



Dr. Hovey's paper was read by Professor Kemp, owing to 

 the former's unavoidable absence. After a brief resume of the 

 geology of the Black Hills District, a series of views was shown 

 illustrative of the extraordinary erosion forms of the schists 

 and pegmatites of the Harney Peak District. His views also 

 showed the tin mines of the Black Hills, in which spodumene 

 crystals of large size have recently been obtained as a valuable 

 source of Lithium, as a commercial product. One spodumene 

 crystal here obtained was thirty feet long. The granite veins 

 have also been described by Van Hise. 



Discussion followed concerning the occurrence of extra- 

 ordinarily large crystals of other minerals. 



The biographical notice of Professor Oliver P. Hubbard, 

 prepared by Dr. Hovey, was read by the Secretary, and will be 

 published with an accompanying list of Dr. Hubbard's publica- 

 tions, in the Ainciica?i Geologist. 



Professor Stevenson, in behalf of the committee appointed to 



