H6 .1. S. DILLEB — SANDSTONE DIKES. 



("row creek narrows, and numerous fossils have been found in the conglom- 

 erate which forms the hills. The conglomerate ie apparently the one which 

 crosses the North fork jus! below the month of Hulen creek and belongs in 

 the Chico aeries. All of the dikes, excepting the one already noted on the 

 North fork three-quarters of a mile below the mouth of Eagle creek, trav- 



• Btrata which apparently overlie the Chico con (Ipraerate. 



Dike "a Squaw Greek. — At 7, on Squaw creek, there is a 1 1-inch vertical 

 dike which Btrikes N. 53° E. The direction of Squaw creek and its gentle 

 Blopes are Buch a- to yield poor exposures of the underlying rocks, and if 

 other dikes are there they are not easily discovered. 



Dikes <>n "Roaring River. —The dike- already noted on the North fork ami 

 on Crow and Squaw creek- are not clearly related to one another — i. e., the 

 same dikes cannot he recognized with ahsolute certainty in two valleys. In 

 a general way it appears that the group of small dikes on the North fork, 

 one mile above Gas Point, represents the group of large dikes at 6 on Crow 

 creek, and they have been so drawn upon the map; but their connection has 

 not been traced, nor can it be easily on account of the soil on the broad 

 divide between. 



< )n Roaring river, however, lic/ms a series of dikes which can he traced 

 for a considerable distance. One of the number, which will he called the 

 Great Dike, can he recognized for aboui '■>'. miles. Itislir-t seen at 8, three- 

 quarters of a mile above the mouth of Roaring river, on the left hank of the 

 stream, with a thickness of 20 inches. Section 2539 is from this dike. Its 

 position was vertical and parallel to the wall. Section 2540 was vertical 

 and transverse, and 2541 was horizontal. The strike is N. 7<>° E., parallel 

 to the gen >ral direction of the valley up which it continues for over a mile. 



Three-fourths of a mile above the first exposure the same dike crop- out 

 again near the west end of Mr. Drew's fields. It stands out prominently, 

 as Bhown in plate 6, figure 2. The strike of this roughly columnar, wall- 

 like mass i- N. 55 E. It is vertical, and 5 feet in thickness. The rock is 

 micaceous, and although hard, is rather easily disintegrated; for this reason 



the rock crop-; out OH sleep slopes, where the erosion is rapid and in 8XCI 38 



of complete disintegration ; but on gentjer slopes, where the disintegration 

 is in excess of transportation,! he dikes do not outcrop and cannot be readily 



traced. The -oft -hah- are here well exposed directly against the dike, and 

 -how no trace of induration. The sides of the dike are somewhat firmer 

 and the -and apparently liner than that in the middle portion. This feature 



has been noticed in a number of cases, and will be referred to again in con- 

 sidering the micr08C0pic Btructure of the rock. It recall- similar phenomena 

 frequently observed in connection with dikes of igi us rock-. The simi- 

 larity i- enhanced by the fact that along it- b irders the dike frequently in- 

 clude- -mall fragments of -hale a feature which ha- been observed in many 



