264 J. F. XEWSOM — CLASTIC DIKES 



stone dikes in granites in the Pikes Peak region in Colorado. The 

 dikes are of tough even grained sandstones, and vary in thickness from 

 films in the granites to masses several hundred feet in thickness, some of 

 which can be traced for a mile. In speaking of them Cross says : 



" The dikes have a general trend parallel to the belt in which they occur. 

 They stand vertical or have a steep dip to the northeast, and often appear as a 

 complex of nearly parallel fissures with many branches and connecting arms. In 

 width they vary greatly. The larger number are a few inches or a few feet thick, 

 but many of the smaller branches thin out to a mere film. On the other hand, 

 several dikes are many yards wide, and two form prominent ridges with a width 

 of from two to three hundred yards each. * * * The larger dikes form ridges 

 with narrow crests rising abruptly three or four hundred feet above the parallel 

 gulches." 



No exjDlanation is given of the origin of the dikes, but Cross suggests 

 that possibh^ the fissures in which they^ occur were formed " during 

 some period of orographic movement," inasmuch as the dike system and 

 the structural axis of the Front ranges coincide in direction. 



Eldridge, 1896. The uintaite (gilsonite) deposits of eastern Utah, 

 which occur as veins, were described by G. H. Eldridge in 1895-1896.* 



Some of the veins are vertical, while others dip at high angles. They 

 have a general northwest strike, and vary in thickness from a fraction 

 of an inch to eighteen feet. The}' vary " in length from a few hundred 

 yards to eight or ten miles," and in strike from north 35 degrees west to 

 north OD degrees west. The,y occur in the Green River limestones, 

 shales, and sandstones. The limestones and shales are largel}^ bitu- 

 minous. Regarding the origin of the veins Eldridge says : 



"The condition in which the gilsonite found its way into the veins seems most 

 probably to have been that of a plastic mass coming from below under pressure." 



Pavlow, 1896. In the Geological Magazine for February, 1896, f 

 Dr A. P. Pavlow describes a sandstone dike which cuts horizontal!}^ 

 stratified gray and black clays near the village of Yavley, in the district 

 of Alatyr, in Russia. 



The sandstone composing the dike contains fossils of Tertiary age, 

 while the clays cut by it are of Lower Cretaceous age. The nearest sand 

 and sandstones of Tertiary age that are mentioned are about 12 miles 

 distant from the dike, and in the southern part of the province of Sim- 

 birsh ; there the Cretaceous beds are overlain by Tertiary sands and 

 sandstones. The surface of the country in the district of Alatyr and 

 about the dike is covered by alluvial sands unlike the sands of the dike. 



* George Holman Eldridge: Tlie uintaite (gilsonite) deposits of Utah. Seventeenth Ann. Rept. 

 U. S. Geol. Survey, part i, Washington, 189G, pp. 909-949. 



f.A. P. Pavlow: On dikes of Oligocene sandstone in the Neocomian clays of the District of 

 AlatjT, in Russia. The Geological 3Iagazine, new series, decade iv, vol. iii, 1896, pp. 49-53. 



