194 A. J. TIEJE 



f Shale ( ?), thin bedded, reddish, arenaceous, muscovitic 2 



(biotite dacite porphyry sill) 25 



e Covered 50 



d Sandstone, much as in bed i; greenish arkose balls from lower beds, or 



else representing coarse sands long rolled about 10 



c Conglomerate, matrix arkosic, pebbles up to 8 in. in diameter, qz. and 

 orth. preponderant, but much granite fine and coarse grained, of 

 both biotite and hornblende facies; also rarer large limestone frag- 

 ments, hard, crystalline, reddish; in nature much as bed u 75 



b Conglomerate, much as in bed c, but with lowest beds merely gritty to 



arkosic, and with many lenses of pebbles up to f in. in diameter. . 25 



a Shale ( ?) finely laminated, dark red; subhard, very arenaceous and fer- 

 ruginous, somewhat calcareous i 



(Unconformable on Granite) 



Analysis of this section does not of course reveal the lateral 

 variation in size of grain, a significant characteristic of the forma- 

 tion; beds wedge out and coarse grain gives way to fine, often in 

 a few feet. It should further be mentioned that north of the 

 Cache la Poudre River appear intercalated limestones, carrying 

 marine fossils and becoming of increasing importance as the 

 Wyoming line is approached. At Colorado Springs, also, some of 

 the sandstone beds are grayish to greenish, and, 475 feet up in a 

 2,000-foot section, a marine fossil, Lingulodiscina, is found in a 

 pocket of green shale. 



Analysis does however disclose other salient characteristics of 

 the Fountain formation, all which must be explained and harmo- 

 nized in an interpretation of the sediments. The main character- 

 istics are (i) absence, anjnvhere in the sequence, of the marine 

 rhythm, conglomerate to sandstone to shale, or vice versa; (2) a 

 consequent great thickness of unassorted, unsized conglomerate and 

 arkose, with only occasional fine-grained arenaceous material; (3) 

 a predominance of subangular and angular pebbles, often of bowlder 

 size, and notable among which are muscovite flakes f inch long,^ 

 fresh feldspar fragments, and bits of limestone; (4) freshness of the 

 feldspar; (5) a pecuhar type of cross-bedding, described below. 



' N. M. Fenneman, op. cit., p. 22, assumes that the muscovite is secondary. S. F. 

 Emmons, U.S. Geol. Surv., Monograph 12, p. 68, had long before recognized it, under 

 the microscope, as primary in large part. 



