5i6 FRANK D. ADAMS 



microscope is exactly that presented on a large scale by many fault 

 planes. 



d) Deformation with alum as an embedding material. — As has been 

 shown, alum is much more ■ resistant to deformation than either 

 parafhne, fusible metal, or sulphur. A series of marble columns was 

 accordingly deformed by Kick's method, employing alum as an 

 embedding material. These were of the same dimensions as before, 

 as were also the copper tubes employed. The maximum loads 

 employed in the several experiments were from 35,000 lbs. to 41,500 

 lbs. The time of deformation was from 15 to 45 minutes. The 

 shape presented by the deformed marble column is remarkable. 

 The column for some distance from either end, in the earlier stages 

 of deformation, remains intact, and these terminal portions are 

 forced toward one another and into the middle portion of the column, 

 which bulges outward, not however with a smooth symmetrical 

 outline but with the development of a curious leafy form, which, 

 when looked down upon from the end of the column, bears a resem- 

 blance to an artichoke. The leaves which wrap closely around the 

 central stalk have well-developed, wedge-shaped points or termina- 

 tions and occur in great numbers. They, however, are not arranged 

 in regular series but each individual leaf has the appearance of over- 

 lapping others which lie beneath it. One of these curious forms is 

 shown in Plate IV, Fig. b, with a column of marble of the original 

 dimensions placed beside it. 



When a vertical section is cut through the axis of one of the 

 deformed columns, the undeformed ends of the column are seen to 

 terminate within the substance of the column in the form of rather 

 obtuse cones pointing toward each other, and these, under the pres- 

 sure, slowly advance toward one another, thin layers of the marble 

 shearing off their faces and being forced outward, thus causing the 

 lateral expansion of the column under deformation. As this con- 

 tinues, the cones at either end become gradually sheared away, and 

 when deformation is very far advanced they eventually disappear. 

 Each little layer of marble, however, as it is sheared off the face of the 

 cone in the line of a tangent to it, becomes cut across by planes of 

 movement along which other layers are being sheared off in the direc- 

 tion of other tangents, so that the whole medial portion of the column 



