ENDucH] WASATCH GKOUP. 81 



A section taken along this creek gave a result which places the thick- 

 ness of the Wasatch Group of that region at about 1,500 feet. It is pos- 

 sible that in this section some beds may be included that ought prop- 

 erly be referred to the Laramie; but the line of separation cannot be 

 drawn with precision, unless as the result of very careful detail studies. 

 Taking the group as I had determined its vertical extent in the field, 

 we find the following result (a being the highest stratum) : 



(a) Yellow sandstones, middle-grained, partly shaly, and con- 

 taining narrow interstrata of dark shales 180 feet. 



(6) Dark greyish-brown shales, containing indistinct remains 



of plants 30 feet. 



(c) Massive yellow sandstone 00 feet. 



{d} Shales varying from light yellow to brownish, sometimes 



almost white with a pink tinge 210 feet. 



(e) Yellow massive sandstones 130 feet. 



(/) Grey and yellowish shales, sometimes quite dark, sandy, 



and containing thin interstrata of sandstones 110 feet. 



(g) Brick-red sandstone, weathering readily ; color constant 



throughout the stratum 160 feet. 



(/i) Eeddish to brown shales 20 feet. 



(i) Sandstones, partly massive, partly shaly, containing thin 



interstrata of shales ,....., 250 feet. 



(Ic) Yellow, grey, and whitish shales and marls 100 feet. 



[l) Heavy beds of yellow to white sandstones 230 feet. 



In the upper members of the Wasatch, beds of coal are found within 

 our district. These are not very extensive, however, nor is the quality 

 a particularly fine one. Admixtures of shale make it " slaty," and upon 

 exposure it readily weathers into small fragments. On Douglas Creek, 

 below Station 36, a rather interesting case was noticed, illustrative of 

 the recession and advance of the water into which some of the sand- 

 stone beds were deposited. A sketch there taken, and reproduced as a 

 section (Section II), will give an idea of the appearance as shown upon 

 the vertical face of a bluff. A slight fault (a) produces a local disturb- 

 ance at the northern end of the section. It is simply a small drop, 

 which is due, probably, to a subsidence produced by the erosion of some 

 of the underlying strata of shales. Alternating sandstones and shales 

 compose the lower portion of the bluff. One ot the former (b) underlies 

 a thin stratum of dark shales (c), which in turn are covered by a bed 

 of white sandstone (d) of varying thickness. Upon this are deposited 

 two strata of coal (e) separated by a thin layer of dark grey, carbon- 

 aceous shales. From the south the waters again encroached upon the 

 land where the coal was being deposited, and we find a stratum of 

 white sandstone, which gradually thins out northward and finally dis- 

 appears entirely, above the coal. A similar thinning out of the upper 

 beds can be observed, that no doubt grow much thicker farther south. 

 The connection was broken at the edge of the bluff and the continuation 

 of the strata not visible. Either by a gradual subsidence of the then 

 existing land or by a rise of the waters from the south this effect was 

 produced. 



An interesting feature of erosive action was observed at several 

 points within the Wasatch area. The famous " monuments" of the 

 Pike's Peak region will be remembered by every one, and also the 

 causes that led and still lead to their formation. We have in the in- 

 stances at present under discussion an analogous case. Instead of sand- 

 stones forming the base and column of the " monument," we here have 

 6 G 



