486 Russell — Relations of the Great 



contain abundant dark minerals, the lode is apt to have a 

 bluish or greenish tinge, apparently derived from their 

 alteration. A thin section of this bluish portion shows 

 remnants of unreplaced minerals. Besides angular 

 altered inclusions of the crystalline rocks, the lode occa- 

 sionally contains small angular or rounded pebbles of 

 quartz, produced by brecciation and grinding. 



This lode is apparently due chiefly to replacement, 

 though parts of it may be actually fissure fillings. As 

 shown by the map (fig. 1), it outcrops at nearly every 

 point where the crystallines and the Triassic are found 

 close together, and its largest exposure, north of Bran- 

 ford, is over half a mile long, and averages over 150 feet 

 vide, not including the slopes of quartz talus. Other 

 outcrops, beyond a concealed stretch, indicate that it is 

 probably over 3,500 feet long. 



3. The fault zone and brecciation. — Near the course 

 of the Great Fault, and for some distance to the west of 

 it, there are zones of shattered and crushed rocks. Brec- 

 cias are of frequent occurrence, and there are zones of 

 rounded basalt fragments embedded in crushed or quite 

 firm basalt. Veins or dikes of sandstone and shale occur 

 in the basalt, and sometimes reach a width of several feet. 

 Large basalt blocks, sometimes hundreds of feet long, 

 have been brought up by distributive faulting from lower 

 horizons, and occur at intervals along the course of the 

 fault. These features are a striking testimonial to the 

 great movement and shattering that affected the region in 

 post-Newark time. 



4. The f agglomerates. — For convenience in mapping, 

 rocks largly composed of pebbles over three inches in 

 diameter, some of which are somewhat angular, have been 

 considered fanglomerates. These rocks are unlike any- 

 thing else observed in the Triassic trough. They are 

 composed of angular bowlders of various sizes, cemented 

 by sandstone. In some places the bowlders are sharply 

 angular, though usually the larger ones are somewhat 

 rounded. The bowlders reach several feet in diameter 

 in several places, and in one place the rock was chiefly 

 composed of hugh bowlders of basalt, several reet in 

 diameter, some of which are vesicular. Both the size and 

 angularity of the bowlders increases quite rapidly 

 towards the Great Fault, though in an irregular manner. 

 The rock is quite variable, contains numerous finer 



