480 



RECORDS' 



E. 0. Hovey, Biographical Notice of Professor Oliver 

 P. Hubbard. 



Summary of Papers. 



Dr. Call's mineralogical notes were preceded by a brief res- 

 ume of the geology of the vicinity of Mammoth Cave. The 

 strata making the geologic section are nearly horizontal, and 

 all the rocks forming the cavern are of sub-carboniferous age. 

 The region of the cavern is capped with sandstones of the 

 Chester Group, 500 feet thick. Under these are oolitic and 

 other limestones, m which the cavern is excavated to a thickness 

 of over 350 feet. The drainage level of the cavern is deter- 

 mined by the present level of Green River. Five different 

 levels have existed during geologic time. No gypsiferous strata 

 are known in the region. The overlying sandstone is usually 

 quite ferruginous ; but no pyrite occurs in either strata. Sec- 

 ondary crystallization has occurred in many of the stalactites, 

 causing them to simulate the fibrous appearance sometimes as- 

 sumed by aragonite. The stalactites of recent origin almost all 

 have a downward-projecting tree root as their origin of fixation, 

 or are beneath sink-holes. The chief objects of mineralogical 

 interest are the gypsum crystals, which cover the sides and 

 ceilings of certain avenues in the cavern, in the upper of the 

 five levels only, and not in any levels now occupied by streams. 

 These crystals are sometimes curiously and remarkably con- 

 torted, and the terminations of the crystal masses are often re- 

 curved in a direction contrary to the direction of gravitation. 

 Occasionally the gypsum assumes a botryoidal form, but is 

 commonly found as needles or aggregated in loose masses of 

 fibrous crystals. The gypsum crystals occur only along cracks, 

 and are built up by increase from the base, while the calcium- 

 carbonate stalactites are always built up by additions to their 

 surface or terminations. It is difficult to account for the large 

 amount of sulphur needed by assuming its origin in organic 

 bodies, such as plants and the forests which are of abundant 

 growth in the region, and have been abundant for geological 

 ages. The origin of the carbon dioxide necessary for the great 



