12 1 .1. S. DILLEB — SANDSTONE DIKES 



At 53, two and two-thirds miles above the mouth of Sail creek, is a dike 

 1 fool in thickness. Section 2522 from this dike was parallel with the side, 

 and 2523 was vertical and transverse. At this point the shales disappear 

 beneath the newer formations, and nothing more is seen of the dikes further 

 doM ti the stream. 



The section so well exposed along Cold fork was examined, hut no dikes 

 were discovered. They do not extend so far southwest. It is likely that a 

 few may appear in Long gulch, which my limited tim< did nol enable me to 

 explore. 



The most southwestern dike observed was seen on the Red Bluff* and Hay 

 Fork stage road, about four miles northwest of Shiveley's I Hunter's 1*. I ). i. 

 The dike is 2 feet in thickness, rather soft, strikes N\38 c E., and its southerly 

 extension is offset to the northwest after the maimer of the dikes on Salt 

 creek. 



General Description. 



The dikes are nearly vertical, wall-like masses of sandstone, varying from a 

 mere film to 8 feet in thickness, and cut directly through the inclined strata — 

 sandstones and shale- — of the Cretaceous group. They vary somewhat in 

 strike from N. 20° E. in the southwestern portion of the series to N. 70° E. 

 near the other end ; and in dip arc usually vertical, but they may be in- 

 clined as much as 65° to the N. W. 



The great majority of them are less than a mile in length, some perhaps 

 less than 100 yards; hut the Great dike, which extends from near the mouth 

 of Roaring river across Poverty gulch, Camp creek, and Middle fork appar- 

 ently to Dry creek, has a total Length of 91 miles. At one point on Middle 

 fork it is * feet thick, but generally about o feet. 



The dikes are parallel to the joints in their vicinity, and BO related to them 

 as to indicate thai the joints have nol been produced by the dikes, but that, 

 on the contrary, the position of the dikes has been determined by the joints. 



The majority of the dikes observed are Btraight, intersecting a Btream- 



blull' from top to bottom, affording an exposure ranging from live to sixtv 



feet in height. By offsetting a Bhorl distance to one side or the other, the 

 dike sometimes exhibits a more or less zigzag course both vertically and 

 horizontally. Others appear to end abruptly before reaching the Burface, 

 < asea have been Been also where a dike apparently ended in its downward 

 course, but Buch have always been found connected with other dikes. In a 

 number of cases dikes have beeu noticed to combine as thej ascend, but no 



examples of combining in tl pposite direction were discovered. 



The shales and sandstones in contact with the dikes are not disturbed by 

 them nor indurated in any «:iv as if by heat, which is frequently the case 

 upon the borders of igneous dik< -. 



