358 DYNAlVnCAL GEOLOGY. 



northern limit of South Carolina. The ranges are from 10 miles in length 

 to about 350 miles ; and their general course is closely parallel to that of the 

 Appalachian Mountains, even to its westward bend in Pennsylvania. They 

 overlie Archaean or Cambro-Silurian rocks. The Connecticut River Range is 

 120 miles long; and the "Palisade Range," extending from southern 'New 

 York, on the Hudson, into Virginia, is 350 miles long. See, further, the 

 account of the American Triassic under Historical Geology. The rocks 

 are solely Triassic in age. The depth of the rocks of the ranges varies 

 from 3000 to possibly 8000 feet. Facts prove that they were laid down in 

 each case in an independent, gradually deepening geosyncline. 



The strata, through the whole 1000 miles, are alike in their essentially 

 fresh-water or brackish-water formation ; in the granitoid origin of the sand- 

 stones and shales, as well as in their general system of structure. 



The dip of the beds is, with rare exceptions, monoclinal, and mostly 

 between 5° and 25° in angle. In the Connecticut Valley, it is 5° to 25° 

 eastward. In the Palisade belt, about the same westward. In two North 

 Carolina belts, the eastern has eastward dip, and the western, westward. 

 Plexures are local, and of rare occurrence. The only marked one that has 

 been reported is a large syncline in the short Richmond basin. 



The rocks are much faulted. But this is not evident in large visible 

 displacements along fractures, but in the striated or scratched surfaces over 

 large areas, which indicate the slipping of bed on bed, and along the surfaces 

 of the numerous small fractures ; sometimes all sides of blocks, even when 

 they are no larger than the hand, are striated. 



All the Triassic areas have their lines of trap-dikes ; and the associa- 

 tion of the igneous rocks with the stratified is so intimate and so extended 

 that the two must have had in some way a common history. The ejection of 

 some of the trap, moreover, preceded the later depositions of sandstone. The 

 trap-ridges, which consist of a large trap-mass, generally 200 to 300 feet 

 thick, underlaid, and partly overlaid, by sandstone, have usually a bold 

 palisade-like front (page 804), of which the "Palisades" on the Hudson are 

 an example, and the name Palisade System is, therefore, an appropriate 

 name for the system of ranges. 



The facts indicate (1) a general unanimity of movement in a series of 

 geosynclines or trovighs that were wholly separated from one another in 

 their rock-making ; and (2) a disturbance that resulted almost everywhere 

 in monoclinal uplifts of low angle, and was accompanied in most parts, now 

 and then, or at the close, with fissure-ejections. There is hence a combina- 

 tion in the Palisade System of eight or ten individual mountain ranges. In 

 the nearly total absence of flexures, the ranges differ from the Appalachian 

 Range, while like it in the preparatory geosyncline of deposition and in the 

 occurrence of great faults. 



The Sierra Nevada Range is supposed to have been made at the close of 

 the Jurassic, or a period later. 



