IRREGULAR SANDSTONE DIKES. 



421 



Near by are five small dikes, each only a few inches in diameter, and 

 varying considerably in strike — from N. 35° E. to N. 55° E. Ascending the 

 stream, two small dikes, 2 and 3 inches thick, are seen at 40, two miles above 

 the mouth of Salt creek, on the left bank ; then follows a stretch of three- 

 quarters of a mile in which none were seen. 



At 41, about one-quarter of a mile below John Allen's, headquarters of 

 the Diamond Range, three excellent dikes appear. The first is 18 inches in 

 width, has a strike of N. 40° E. and dips 85° N. W. It is represented in 

 plate 7, figure 3, which shows distinctly two sets of fractures common in these 

 dikes: (1) Cross-fractures dividing the mass horizontally and vertically into 



i * 



Figure 4. — Crooked Sandstone Dike, is Inches In Thickness. 

 On Dry creek, five and one-half miles above the mouth of Salt creek. 1 = Dike ; 2 = Shale. 



more or less regular 6-sided blocks; and (2) divisional planes parallel to the 

 .sides of the dike, separating it into thin plates. The shales here as else- 

 where are neither altered nor disturbed near the contact. Specimen 2404 

 was collected from the edge and 2405 from the middle of this dike. 



Near by is another dike of the same size and position, which is especially 

 remarkable on account of* its distinct vertical banding parallel to its sides. 

 Similar banding has been seen in other dikes, but nowhere else so distinctly. 

 The banding is due to the parallel arrangement of coarser and finer sand, 



