Blasdale. ] 



Contribution to Mineralogy. 



347 



tion of the rock. This theory would explain their rounded charac- 

 ter, and is supported by the occasional occurrence of nodules with 

 indications of such a center of crystallization, but other facts are not 

 in harmony with this view. The evidence seems to point to the 

 fact that the actinolite is all derived from the crystalline schist. 

 In no instance were the nodules found in the serpentine, and there 

 was a striking absence of actinolite-containing fragments below the 

 serpentine areas. Also the characters of the actinolite from the 

 schist and from the nodules are identical, the variations in the form 

 and size of the crystals, their deformations (curvatures, etc.), are 

 repeated in both, the chemical composition is essentially the same, 

 and the associated minerals show the same range of variation. 

 There is, however, insufficient evidence of the separation of the 

 nodules as distinct structures in the original schist, though sugges- 

 tions of this are furnished in the lenticular or pocket-like masses 

 occasionally encountered. 



A dynamical theory would require the action of forces capable 

 of disintegrating the schistose rock, and of grinding or shearing 

 forces capable of rounding and polishing the more or less angular 

 fragments thus produced. Examination of all the actinolite- 

 containing fragments of a given area shows that only a part of 

 these have attained the perfect boulder form ; they are often 

 present as angular or only partly-rounded fragments, many of 

 which show a suggestion of the schistose structure. Furthermore, 

 those areas which show the greatest number of perfect actinolite 

 boulders also show rounder masses of other minerals (glaucophane, 

 etc.), though the former are decidedly more frequent. The latter 

 facts may be due to differences in the resisting powers of the differ- 

 ent minerals to the agencies concerned. The nature of the agency 

 concerned in such a grinding and polishing process is somewhat 

 difficult to indicate. Streams of water of high velocity could 

 readily accomplish the desired result, and occasional boulders, 

 which were found in the bottom of stream beds, possessed the 

 rounded and polished character in a high degree, but, presumably, 

 this agency is of too local a character to account for all the phe- 

 nomena. Aside from this there is evidence of intense movement 

 and shearing action of the rock mass in the crumpled character of 



