414 J. S, DILLEB — SANDSTONE hlKl- 



nuinbers are omitted. Ii is probable also that there are a dumber of undis- 

 covered dikes doI represented upon the map. The Bhales in the banks of 

 the streams must be well exposed in cliffi or the dikes they contain will 

 not outcrop. Along a portion of Squait creek and near the mouth of Middle 

 fork the banks are so low and covered with soil that dikes, even if they do 

 occur there, would nol be exposed. 



Dikes mi the North Fork. — At 1 ou the map, three-quarters of a mile below 

 the month of Eagle creek, there is an L8-inch dike of micaceous sandstone 

 well exposed in a portion of the creek bed and part way up the northern 

 hank, but upon the southern slope it was not found. The strike of the dike 

 is N. 15 lv. and the dip 7~>° to the N. W., and of the adjacent sandstones 

 and .-hales of the fossiliferous Eorsetown beds the strike is about N. 10° W., 

 and the dip 15° to the N. E. 



The dike is so inconspicuous as a topographic feature that it might be 

 easily passed by without being discovered, and yet it is sufficiently well 

 exposed to show its relations clearly. It is the northwesternmost dike of the 

 region, being four and three-quarters miles from the nearest dike further 

 down the creek. 



( )ne mile above <ia- Point, at 2 on the map, there is a group of six small 

 dikes, the most important of which are represented in plate 6, figure 3. The 

 largesl vein is four inches thick and traversed by many cross-fractures which 

 give it a columnar aspect. The three veins combine as they ascend the 

 bank, hut soon run out and fail to reach its summit. The small vein upon 

 the right diminish.- downwards to a mere film, sometimes disappearing alto- 

 gether, although the joint fissure which it occupies is well developed. Traces 

 of joints may be seen in the shale to the right of the dikes, and some of them 

 contain thin films of line micaceous sand exactly like that of the larger 

 dikes. The plane of stratification in the shales is distinctly marked by vari- 

 ation in the sediment, as well a- by lines of calcareous nodules, and it ap- 

 pears that there has been no faulting along the dikes. The boundaries of 

 \\\<- larger dike- are generally well denned, as are also those of many small 

 ones, Inn near the tapering edges they are frequently difficult to recognize. 



A -hort distance to the I. -ft of the above vein there is another 2-inch vein 

 which suddenly disappear upwards ; and near by IS the 1-inch vein repre 

 sented in plate 7. figure 2, traversing a bluff •'!'» feet in height. A few feet 



to the right of the dike and parallel with ii i- a well-developed joint. The 



dikes are generally vertical, but this one inclines 65 to the N. W., which is 

 tin- greatest divergence from the vertical position observed. The general 

 inclination of the shale at this point i- about 15° to the southestward. 

 Opposite Gas Point, at 3 on the map. tier, i- a I 1-inch dike which is 



• All dlraotlom recorded In thU paper are magnetic. The variation f<T thai region I 



