FISSURES, OR FRACTURES. 



222 



20,000 feet. In Southwest Virginia, accord- 

 ing to Rogers, there is a line of fracture ex- 

 tending parallel to the Appalachian chain 

 for eighty miles, in which there is a vertical 

 slip of 8,000 feet,* the Lower Silurian being 

 brought up on one side until it comes in con- 

 junction with the Lower Carboniferous on 

 the other (Fig. 196). In Western Pennsyl- 

 vania, according to Leslie, there is another 

 fault extending for twenty miles, in which 

 the lowermost of the Lower Silurian is 

 brought up on a level with the uppermost of 

 the Upper Silurian, the whole Silurian strata 

 being at this place 20,000 feet thick, so that 

 one may stand astride of the fissure with one 

 foot on the Trenton limestone (Lower Silu- 

 rian), and the other on the Hamilton shales 

 (Devonian). f On the north side of the 

 Uintah Mountains there is a slip, according 

 to Powell, of nearly 20,000 feet. J The Sevier 

 Valley fault, Utah, may be traced partly as a 

 slip, partly as a monoclinal fold, for 225 miles 

 (Gilbert). On the west side of the Wahsatch 

 range there is a fault of 40,000 feet (King),* 

 and on the east side of the Sierra one of at 

 least 15,000 feet. || 



But nowhere on this continent, or per- 

 haps in the world, are fissures and faults de- 

 veloped on so grand a scale as in the high 

 Plateau region, i. e., the region bounded by 

 the Wahsatch, the Uintah, and the Colorado 

 Mountains. The whole of this elevated re- 

 gion is traversed by a system of north and 

 south fissures, extending for hundreds of 

 miles, by which the almost horizontal strata 

 are broken into huge oblong prismatic blocks 

 many miles wide. The slipping of these 

 blocks, some to a higher and some to a lower 

 level, with a difference of 1,000 to 5,000 feet, 



* Dana's Manual, p. 399. f Manual of Coal, p. 147. 

 % Exploration of Colorado River, p. 156. 



* Survey of the Fortieth Parallel, vol. i, pp. 728-746. 

 || Le Conte, American Journal of Science, vol. xvi, p. 



101, 1878. 



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