522 FRANK D. ADAMS 



ously complicated manner, but there no plastic flow was discernible. 

 The rock under the conditions of the experiment acts essentially as 

 a brittle body. 



E. dolomite: COCKEYSVILLE, MARYLAND 



This is a typical dolomite, the analysis showing that the carbonates 

 of lime and magnesia are present very nearly in their molecular 

 proportions. It is white in color, practically free from impurities, 

 perfectly crystalline, of medium grain, and is extensively employed as 

 a building stone. 



A column when deformed in parafhne wax in the usual manner 

 was found upon the completion of the experiment to have assumed 

 the same form as in the case of Carrara marble. The upper portion, 

 where the deformation was greatest, showed very plainly two sets of 

 lines crossing its surface and intersecting at angles of about 60°. 

 The upper end of the column at a number of places was commencing 

 to shear down in triangular-shaped masses. From the portion of the 

 column where the deformation had been greatest a series of thin 

 sections was prepared. When these were examined under the micro- 

 scope the rock was seen to be traversed by many little branching 

 lines of finely granulated material, which lines however intersected, 

 giving a rude, diamond-shaped network. The individuals com- 

 posing those portions of the rock between these lines were somewhat 

 flattened in shape and showed distinct strain shadows. 



The dolomite was then deformed in alum in the usual way, the 

 load required being 33,000 lbs. The deformed column presented a 

 striking appearance and showed in a most beautiful manner on its 

 surface the leaflike forms due to movements along Luder's lines, 

 described in the case of the Carrara marble, but the dolomite is seen 

 to be somewhat less plastic than the Carrara marble, for in several 

 places the column was torn by the movement in directions other than 

 those followed by Luder's lines, this tearing giving rise to open and 

 ragged rents in the substance of the column after the alum had been 

 dissolved away. The form is very suggestive (Plate VI, Fig. h). The 

 rock moved as an exceedingly stiff, semi-plastic mass. The upper 

 portion of the column is commencing to shear off along a plane 

 inclined at an angle of about 60° to the horizontal. The movement 



