646 DIALLAGE ROCK. 



eompanying strata, and partly by its alternation 

 with these; while, in a few instances, it is per- 

 fectly distinct ; the strata, at the same time, being 

 prolonged in a parallel direction to the general 

 bearing, and dipping in the same manner as those 

 of the neighbouring rocks. 



The strata of diallage rock are intersected in 

 all directions by innumerable joints, from which 

 their frequent obscurity arises. From this cause, 

 the protruding surfaces present an aspect re- 

 sembling that which is exhibited in similar cir- 

 cumstances by granite ; an appearance which 

 has probably given rise to the opinion that it was 

 an unstratified substance. This feature is very 

 remarkable in the abrupt cliffs ; which are broken 

 in an irregular angular manner, by fissures so 

 numerous and extensive, as to confound all ap- 

 pearance of stratification. 



As this rock alternates, on the large scale, 

 with the primary schistose strata before men- 

 tioned, so it frequently contains minute beds of 

 micaceous schist, chlorite schist, and talcose 

 schist ; more rarely, of hornblende and actinolite 

 schists. In the same manner it is found to in- 



