138 BULLETIN OF THE ESSEX INSTITUTE. 



with the Ute fault series. That these fissures, unlike the 

 relatively narrow ones described by Diller in California, 

 have not been filled from below becomes perfectly obvi- 

 ous when we reflect that the inclosing rock formation is 

 a deep-seated phitonic. The homogeneity and purity of 

 the sandstone, and especially the absence of feldspathic 

 or argillaceous material, make it impossible to regard the 

 dike rock as a fault breccia or as due in any way to the 

 comminution of the wall rock. Ruling out this theory, 

 and infiltration, we are forced to the conclusion that the 

 fissures have been filled from above. But of this theory 

 two principal forms naturally suggest themselves. First, 

 the fissures antedate the deposition of the sand, existing 

 as cracks in the sea-bottom which were filled by the slow 

 process of sedimentation. Second, the cracks post-date 

 the deposition of the sand, but antedate its lithifaction to 

 form a firm sandstone ; and the unconsolidated sand sub- 

 sided and flowed down into and filled the fissures. As 

 Cross has pointed out, the necessary slowness of the 

 process is a valid if not a fatal ol)jecti()n to the first view ; 

 and it also fails to account for the very general absence 

 of stratification in the dikes and of more or less water- 

 worn fragments of the wall-rock. Furthermore, if these 

 traps for sediments opened on the marginal portion of 

 the sea-floor, coarse material washed into them would be 

 protected from further attrition, and the observed fineness 

 and homogeneity of the dikes could not exist. 



By this process of elimination we are forced to the 

 consideration of the view that the fissures were formed 

 after the granite had been covered by the sedimentary 

 deposits and before their complete consolidation, the un- 

 consolidated portions naturally contributing to the filling 

 of the fissures and the formation of the dikes. In the 

 opinion of the writer this view is not, a priori, improb- 



