

FACTS ABOUT MOUNTAIN REGIONS. 791 



Other great fractures that were never opened so as to become veins 

 are indicated by the existence of an extensive displacement or fault 

 along them. The fault toward the western limit of the Green Moun- 

 tains is mentioned on page 214 ; and others, of still greater extent, 

 in the Appalachian region to the southwest, on page 399. From a 

 recent observation by J. G. Lindsley, it appears that the fault re- 

 ported to occur at Rhinebeck, on the Hudson, and to be connected 

 with the Green Mountain region, occurs really at Rondout, on the 

 west side of the Hudson ; that there is here unconformability between 

 Lower Silurian and Lower Helderberg beds ; and that the upturning 

 and faulting of the latter may have taken place, as T. Nelson Dale 

 suggests, when the Catskill plateau received its high position. 



According to King, a fault of 40,000 feet exists in the Wahsatch 

 range. It extends for " 100 miles from north to south," following the 

 axis of a great fold ; and, when made, the western part of the arch 

 sunk to the depth stated. 



Again, the fractures connected with mountain-making sometimes 

 give exit to igneous eruptions. But these deeper fractures have oc- 

 curred where there was little done in the way of folding ; the more 

 of one, the less of the other. It is not known that there were any 

 such outflows in the making of the Appalachians, while they were of 

 great extent and made many trap ranges in connection with the dis- 

 turbance of the Triassico- Jurassic beds of the Atlantic border, and 

 were vastly more extensive over the globe in Tertiary times. 



Besides these great fracturings, there are all grades, down to local 

 breaks in beds and displacements of masses ; and still further, to crush- 

 ings and shovings, and tumblings together of the broken fragments. 



The region of the Colorado basin, and other portions of the dry 

 country west of the summit of the Rocky Mountains, are particularly 

 good for the study of fractures and faults, as well as flexures, because 

 the earth's ribs are there bare of vegetation, and hence open almost 

 everywhere to inspection. The reports on these regions by Powell, 

 Gilbert, Howell, and Hayden, contain numerous illustrations. The 

 parts into which the formations over hundreds of square miles have 

 been broken by the disturbing forces lie together, pitching in yarious 

 ways, with the outlines so well preserved, in spite of erosion, that but 

 little study is required to restore to the mind the original unbroken 

 condition of the beds. Powell speaks of many areas " where a zone 

 has been broken into blocks, and these blocks tipped and contorted in 

 diverse ways and directions, like the blocks of ice crowded in an eddy 

 of a river at the time of its spring flood." 



