HAYDEN.] 



GEOLOGY MIDDLE PARK. 81 



As we descended tlie moiintain-rido'e into tlie valley of the Blue, soon 

 after passing the summit, we found the quartzites of the Dakota group 

 apparently resting- directly on the schists, and as we descend the gently 

 sloping east side we here find sections of the full series of CreLaceous 

 beds inclining not more than from 5° to 8°. As far as the eye could 

 reach, from Mount Powell northward, the quartzites of the Dakota 

 group laid over the east side of the ridge like the roof of a house. On 

 the east side of the Blue there is a high Cretaceous ridge, mostly above 

 the Dakota group, penetrated in numerous places by dikes, out of which 

 great masses of basalt have flowed over the surface. The river itself 

 for a distance of nearly 20 miles to its junction with the Grand flows 

 over the black-clay shales of No. 4 and the dark-gray calcareous shales 

 of No. 3, following a monoclinal interval. 



The terraces along the Blue Elver are quite noticeable. There are 

 two principal ones, but these not unfreqnently break up for short 

 distances into several smaller ones. On the east side of the Blue 

 Eiver, near the junction with the Grand, and on the north side of the 

 Grand, are isolated, low hills of granitic schists, around the sides of 

 which the Cretaceous clays are elevated at moderate angles. As we 

 ascend Grand Eiver even the Dakota group thins out to a considerable 

 extent, so that in some localities it is quite probable that the entire Cre- 

 taceous group is wanting, and the lignitic strata repose on the schists. 

 Above the junction of the Muddy the valley of the Grand reveals a 

 good thickness of the lake-deposits. The terraces are also quite well 

 marked, rising sometimes 80 to 100 feet above the bed of the river. 



MIDDLE PARK. 



The geological structure of the Middle Park has been so carefully 

 studied by Mr. Marvine that I will pass over it very briefly. The geol- 

 ogy is very complicated and of great interest; but in order that it may 

 be clearly understood, it must be presented in great detail with illus- 

 trations. This Mr. Marvine was able to do. In 1869 I spent a few days 

 in the park, and the results form one of the chapters in my annual re- 

 j)ort of that season. 



The variegated beds occur in the southwest portion of the park near 

 Prazer Eiver, beneath the Cretaceous group, and though far less con- 

 spicuous than on the east side of the front range, are undoubtedly of 

 Jurassic age. Near the hot springs there is a high hill, sometimes called 

 Mount Bross, to which I directed attention in 1869. It is composed 

 almost entirely of beds of the Lignitic group, 1,800 to 2,000 feet high 

 above Grand Eiver. 



Prom this hill we obtained a great variety of fossil-leaves characteristic 

 of the Lignitic group. Prom this group in the Middle Park Mr. Lesqureux 

 has identified Sapindus angust'ifolius, Staphylea acuminata, Planera longi- 

 folia, Bhus drymeja, Grlyptostrohus europacus, Sequoia angustifolia, 

 Fraxinusprcedicta, tllmus tenuinerms^Myrica acuminata, Ilex splienophylla, 

 Pterocarya americana, Elms Haydeni, Myrica latiloha. Of the above- 

 mentioned species S. aufjustifolia and Planera longifoUa occur in ac- 

 knowledged Tertiary strata near Elko Station, Nevada, and the former 

 i'fe also found in the South Park. Ilex splienophylla occurs at Green Eiver. 

 The Glyptostrohus europaeus is found at Port Union and in the arctic 

 regions, and is regarded as a Miocene species. So far as we can judge 

 from the fossil-plants, this great series of strata in the Middle Park must 

 belong to the Lignitic group, and is probably of Lower Tertiary age. 



On the north side of the Grand Eiver, about the source of Trouble- 

 G G s 



