SANDSTONE DIKES OF UTE PASS, 145 



Two other modes of occurrence of sandstone are, in 

 the opinion of the writer, suflSciently dike-like to demand 

 recognition here. One of these is that described by 

 Prof. J. D. Dana,'* in the quartzite of Dutchess Co., N. Y., 

 where the rock between vertical joint or shear planes has, 

 perhaps before its complete induration, been reduced by 

 compressive and shearing movements to a structureless 

 mass of sandstone — a dike of sandstone in walls of sand- 

 stone, a species of crushed zone, dike-like structurally 

 but not dj^namically or in the sense of being intrusive. 

 Professor Dana says, "The obliteration of the bedding by 

 impulses of lateral pressure is well illustrated in the 

 quartzite near Poughquag, where the bedding is beauti- 

 fully distinct and nearly horizontal. In two or three 

 places, in the course of a long section of the well strati- 

 fied beds, there are narrow vertical portions of the whole 

 height of the section exposed, which have lost entirely 

 the bedding, and are divided only by vertical joints." 

 Such a vertical strip "looks a little way off like a dike of 

 igneous rock, yet it is only a narrow vertical section of 

 the stratified quartzite, in which, under the lateral pres- 

 sure, fractures were produced, and where, consequently, 

 the successive movements shook down and re-arranged 

 the sands adjoining, so as to obliterate the planes of bed- 

 ding and substitute vertical planes." 



The other mode of occurrence of sandstone in dike 

 form is really one phase of unconformity, where sedi- 

 ments deposited over an eroded surface fill fissures and 

 chasms of various forms. Later erosion may remove the 

 sedimentary deposit and leave the ancient floor intact, 

 with the dike-like roots of the sediments remaining in it. 

 Irving^ has described and fio^ured sandstone dikes of this 



« Am. J. Sci. (3) :), 181-18-2. 



6 Mouographs U. S. Ueol. Survey, v, -292-3. 



