VERTICAL STRUCTURE IN THE DIKES. 423 



upon one side. At 46 is a 6-inch dike, which is very lamellar, splitting 

 parallel to the sides of the dike. Section 2524 from this dike is vertical and 

 transverse, 2525 is horizontal, and 252(3 is vertical and parallel to the sides 

 of the dike. A 2-inch dike near by contains but little mica, aud that not 

 distinctly oriented ; but in the next dike, near 47, mica is more abundant 

 and distinctly arranged parallel to the sides of the dike. This dike is 20 

 inches through, and like a number of others is without any ripple-like 

 marks upon its sides. Near by is a 2-inch dike; and three hundred yards 

 further down the gulch a 15-inch dike occurs which is very soft and rotten, 

 showing spheroidal weathering. 



About a quarter of a mile above the mouth of the gulch the last dike was 

 seen. It is 1 foot thick, very soft, crumbles in the hand, and is full of mica 

 arranged parallel to the sides of the dike. Near by is an exposure of two 

 small dikes in joints. One terminates upwards and the other downwards 

 where the joints end. 



Dikes on Salt Creek, etc. — To the southward the number of dikes "gradually 

 decreases. Ten are exposed on Fight gulch, but on Salt creek there are 

 scarcely half a dozen. At 48, four miles above the mouth of the creek, the 

 largest occurs. It is 3 feet in diameter, strike N. 40° E., stands vertical, and 

 is exposed for 60 feet. Specimen 2519 was collected here, parallel to the 

 sides of the dike, and section 2520, perpendicular. The scales of mica which 

 it contains are arranged parallel to the sides of the dike. It is somewhat 

 banded vertically, and its sides are rippled parallel to the line of contact 

 with the bedding planes in the adjoining shales. The ripples are about an 

 inch in width ; their crests are somewhat rough, while the intervening portions 

 are smooth. 



Three hundred yards down the creek, at 49, is another dike, 21 feet thick, 

 containing an abundance of mica scales arranged parallel to its sides. The 

 strike of the dike is N. 35° E., parallel with the course of the stream at 

 this joint, and it is exposed at several places, showiug apparently a promi- 

 nent offset to the eastward. A small dike near the large one sends several 

 lateral projections into the adjoining shales. At 50 an l<S-iuch dike appears, 

 and can be traced down the creek for quarter of a mile. The ripples on 

 the sides of the dike run vertically. Upon its northwestern side is another, 

 about 4 inches in diameter. 



At 51, opposite McNett's, a 1-foot dike appears ; strike, N. 40° E. It is 

 much fractured, showing no tendency whatever to break into regular forms. 



A fourth of a mile below McNett's the shales are much disturbed, and 

 here two small dikes occur. One of these, traversing a thin sandstone, ends 

 above aud is apparently cut off below. The other, a 6-inch dike, which 

 splits easily into thin plates, appears somewhat as if displaced with the 

 shales. 



