19G proceedings: geological society 



Experiments with loaded crystals of potassium alum show that these 

 crystals will lift their loads during growth, even if unloaded crystals are 

 present, as long as the conditions of growth are controlled. The essen- 

 tial point to be considered is that the measure of lifting is the depth 

 of whatever "cavities" may form on the upper or lower surfaces of the 

 loaded crystal. With large crystals these height increments are ^ery 

 small compared to the growth on the top surface of an unloaded crystal 

 and hence were probably overlooked in comparison with the latter. 

 Other factors entering into the lifting effect produced are the relation 

 of load to the crystallographic direction, and the habit of the crystal. 

 The mechanism by which this lifting takes place is not at present 

 known. Taber's view is that the lifting is caused by the expansion 

 which takes place when the solid separates from the film of solution 

 which is assumed to be always under the supporting edge of the crystal. 

 Unfortunately, the experimental difficulties involved in testing this con- 

 clusion have not been overcome, so that the matter is unsettled. An- 

 other possible explanation is that the lifting effect is an expression of 

 those forces responsible for crystal development. The experimental 

 results obtained with crystals with painted surfaces indicate this ex- 

 planation. 



Discussion: E. T. Wherry ' described examples of fibrous crystals 

 produced by crystal interference. 



J. W. Gidley: The origin of the mammals. (No abstract.) 



Discussed by R. S. Bassler. 



The 315th meeting was held at the Cosmos Club, February 14, 1917. 



INFORMAL COMMUNICATIONS 



H. E. Merwin: Diffusion and crystallization of metallic copper in 

 crystalline sulphides. After cooling from a molten state in a vacuum 

 copper-iron sulphides may contain an excess of copper which slowly dif- 

 fuses and crystallizes at ordinary temperatures. The growing crystals 

 of copper open cracks in the solid mass in which they form. 



REGULAR PROGRAM 



D. F. Hewett: The origin of bentonite and the geologic range of re- 

 lated materials in Bighorn basin, Wyoming. Bentonite is a drab and 

 cream colored bedded clay which until recently has been recognized 

 only in the upper part of the Benton formation in Colorado, Wyoming, 

 and Montana. Work on the west side of Bighorn Basin has shown 

 that bentonite and clays closely resembling it occur at intervals from 

 the base of the Benton formation of the Colorado group to the top of 

 the Meeteetse formation or upper part of the Montana group. The 

 beds occur, therefore, in a stratigraphic range of about 5500 feet in 

 Bighorn Basin. A clay that closely resembles bentonite is also inter- 

 bedded with tuffaceous rocks in an upper Eocene formation near Owl 

 Creek. 



In order to determine the mineral constituents of bentonite, six spec- 

 imens were sized by the Bureau of Soils, and the proportions of each of 



