EXTENSION OP THE GREAT DIKE. 419 



of the stream, it does not continue all the way across, but is cut off by shales 

 which crop out directly in front of the dike. Whether or not the dike was 

 offset to one side I could not discover. Specimen 2531 was collected here. 



About 300 yards northwest of the line of the Great dike, at 21, a mile 

 above Miller's, a 5-foot dike is well exposed; strike N. 41° E. It includes 

 numerous fragments of shale, some of which are several inches across. 

 Two small quartz pebbles were found in this dike, but otherwise the dike 

 material was like that in all the other dikes. The fragments of shale were 

 not distinctly oriented in the dike and gave a prominent pitting to the weath- 

 ered surface. Within fifty feet to the northwestward are three other dikes, 

 ranging from 4 to 5 inches in thickness. 



Above Miller's a mile and a quarter, Middle fork passes through a small 

 narrows between ledges of conglomerate. At the irrigating dam just below 

 the narrows the micaceous sandstone (specimens 2532 and 2533) interstrati- 

 fied with the shales and conglomerates looks very like the rocks found in the 

 dikes. It is well exposed in a side gulch, and strikes N. 24° W., dipping 32° 

 to the N. E. The strike and dip are not uniform here, for the conglomer- 

 ate by the narrows strikes N. 37° E. and dips 47° 8. E. , and at another place 

 near by the shales strikes N. 5° E. and dip 33° S. E. 



Above the narrows, at 22, on the right bank of the stream, are three 

 vertical dikes, 14 inches, 2 feet, and 3 feet, respectively, in thickness. The 

 last apparently represents the Great dike with which it is in line, striking 

 X. 40° E. 



At 23 two other dikes appear, one of 2 feet and the other of 15 inches 

 with offsets to the northwest as it asceuds. At 24 is a 12-inch dike exposed 

 in the bed of the stream; strike N. 39° E. A little further up Middle fork 

 a gulch enters from the south, and in it (at 25) this dike crops out a second 

 time with a thickness of 6 inches. 



On the opposite side of the stream, at 20, is a rather heavy dike, which can 

 be traced for 300 yards aud appears to be the continuation of the Great 

 dike. It crops out again at 27, where it is 2\ feet thick and strikes N. 45° 

 E. Continuing to 28, it disappears in the south bank with a thickness of 1 

 foot. From this point to its most northeastern exposure on Roaring river is 

 about 6 miles, in which distance there are 15 exposures of the Great dike. 

 It may not be a continuous dike all the way. More likely it is a series of 

 dikes very nearly in the same line. 



At 27, on the southern side of the Great dike, is a small one 14 inches in 

 diameter. Where next exposed further up the stream it is of somewhat 

 smaller size. 



At 29 are three small dikes, one of which is 6 inches and the others 2 inches 

 each in thickness. These are followed by two 4-inch dikes at 30 ; and again 

 at 31, about 4 miles above Miller's, by one 2 feet in diameter. 



LV— Bum,. Gf.oi,. Soc. Am.. Vol. 1, 1889. 



