520 FRANK D. ADAMS 



nail of the same dimensions as the former one being inserted in the 

 hole made by the latter. 



B. LITHOGRAPHIC LIMESTONE: SOLENHOFEN, BAVARIA 



This is a buff-colored limestone of extremely fine and absolutely 

 uniform grain, containing about 3^ per cent of various impurities. 

 It breaks into a splintery or conchoidal fracture. When a column of 

 this rock is deformed in parafhne the result is similar to that obtained 

 with Carrara marble, and in almost every case the same transverse 

 cracks develop upon the removal of the embedding material. 



In an experiment in which the rock was deformed in alum the 

 column presented one of those highly interesting forms sometimes 

 seen in deformed Carrara marble, dolomite, etc. This is produced 

 by the development of a complete system of minute parallel faults 

 crossing the column at an angle of 65° to the horizontal. The upper 

 portion of the column thus tends to shear down along these planes, 

 the rock however remaining hard and solid, indicating a deformation 

 under conditions intermediate between those of the zone of fracture 

 and the zone of flow, but more nearly approximating those of the 

 latter. 



C. FOSSILIFEROUS LIMESTONE: BELGIUM 



This is a dark-gray, highly fossilifeirous limestone. 



A column was embedded in alum and deformed in the usual 

 manner. The height of the column was reduced from i . 574 inches to 

 1 . 4 inches, and the column yielded to pressure in such a manner that 

 instead of bulging symmetrically it developed a movement exactly 

 like that described in the experiment with Solenhofen limestone; that 

 is to say, the upper portion of the column moved down over the lower 

 portion at an angle of about 45°, the movement being concentrated 

 along a strip about half an inch wide. In this strip there were several 

 parallel planes in which the movement was especially pronounced, 

 but within this zone the whole mass was seen to have been more or 

 less plastic. Thin sections of the rock in this portion of the column 

 when examined under the microscope showed little lines of minutely 

 granulated material, often presenting a minutely brecciated structure, 

 the whole constituting a species of "distributed fault." The rock 

 after deformation was apparently as hard and solid as before. 



