490 Russell — Relations of the Great 



The great half-saucer-like folds which give the out- 

 crops of the basalt flows their crescentic outline are one 

 of the most remarkable features of the structure of the 

 region. They vary in diameter from about 1,000 feet, 

 in the vicinity of North Guilford, to many miles. As they 

 all have the same relations to the Great Fault, and all die 

 out rapidly west of it, they appear to be connected with 

 its formation. Possibly they are due to unequal subsi- 

 dence along the fault plane. If this were the case, there 

 would be no tendency for the fault plane to advance to the 

 west in the upwarps. 



A normal fault, such as the one under consideration, 

 probably had some dip to the west at its origin, and this 

 would probably be increased by the tilting of the region. 

 The faults of the central portion of 'the Triassic dip both 

 northwest and southeast, while those near the Great 

 Fault, which are probably shear faults more or less 

 parallel to it, dip only to the northwest, and dip steeper 

 where the dip of the fault was not affected by the tilting. 

 The occurrence of a precipitous eastern slope and a 

 gentle western slope in the great outcrop of the quartz 

 lode north of Branf ord, together with the apparent band- 

 ing dipping west at about 30°, all point strongly to a west- 

 ward dip of the fault plane. Moreover, in the actual 

 exposure of the fault plane found by Davis at Highland 

 Park the dip was 55° W. It is also reported that a well 

 drilled in the Triassic near the fault penetrated the crys- 

 tallines. For these reasons it is believed that the fault 

 plane dips to the west at an angle of from 30° to 60°. 



The relative Dates of Faulting and Sedimentation. 

 The evidence of the Quartz Lode and the Fanglomerates. 



The fact that the quartz lode follows closely the out- 

 crop of the Great Fault indicates that it was formed by 

 solutions that travelled along its plane. The great size 

 of the quartz lode along the fault; the total absence of 

 anything resembling it in the Triassic; its general 

 character and striking similarity to the great quartz mass 

 at Lantern Hill, Connecticut, which is thought to have 

 been formed by heated magmatic waters, 4 all render it 

 probable that the quartz lode was also formed by heated 

 magmatic waters, most likely at the close of the Appala- 

 chian Revolution. 



