ENDUCH.J EED BEDS JURA. 73 



and their western edge follows a southwesterly direction. In 1876 1 first 

 noticed them from Station 2. which is located at an elevation of 9,283 

 feet on Dakota sandstone. There the red sandstones appear in the steep 

 canons immediately adjacent, showing small local faults. They have a 

 general dip to the westward of about 6° to 8°, which is sometimes 

 varied, however, on account of disturbances. Continuing southward 

 they gradually rise to higher elevations until their highest point within 

 our district is reached at Station 3, an altitude of 9,904 feet. Eidges 

 and caSons extending southward are composed of strata belonging to 

 the same group. In the deep canons southeast of the station the Car- 

 boniferous beds crop out, but are soon covered by younger beds. Far- 

 ther east, in Marvine's district. Carboniferous strata cover an extensive 

 area, but in our section they appear only as small exposures in the deep- 

 est canons. 



From that point on, the Eed Beds follow a line of exposure about 

 southeast, parallel in its general course with the Great Hogback Eidge. 

 The sandstones eastward run up high on the slopes of the hills, reach- 

 ing a thickness there of about 2,000 feet. A section (Section I) taken 

 a little north of Station 2, shows the general vertical distribution of 

 the strata, and a small fault, about 61)0 feet in height, one of a num- 

 ber occurring in that locality. Massive beds of red sandstone (a) 

 are overlaid by a series of grey shales and marls (6), interstratified with 

 thin beds of sandstone. These belong to the series that is generally 

 quoted as Jurassic and has been so colored on the map. Yellow and 

 whitish sandstones (c) of the Dakota Group occur above the light-grey 

 marls, and are in turn covered by the Colorado shales (d). Above the 

 latter follow the younger members of the Cretaceous, reaching the Fox 

 Hills group. In spite of the disturbances produced by faulting, the gen- 

 eral westerly dip is noticeable throughout, and is in perfect conformity 

 with under- and over-lying strata. 



Jura. — Beds that have heretofore, more from their relative position, 

 perhaps, than from any direct evidence, been referred to this formation, 

 occur throughout the entire length of the Triassic outcrop. The beds, 

 composed of light-grey marls, shales, and partly sandstones, overlie the 

 red sandstones, and share with them in the disturbances and faults that 

 have taken place. Along the western border of the Triassic outcrop 

 the Jurassic exposure forms a long narrow strip, extending from the 

 White down to Grand Eiver. No fossils whatever were found in the 

 marls that could furnish any clew as to the geological age of the series. 

 As stated above, their position has been assigned to them long ago, 

 partly on account of some fossils found in the same beds east of the 

 Front Eange, partly on account of their position between the Eed Beds 

 and the undoubted Cretaceous. It is no more than fair to state that their 

 being placed into the relative position they at present occupy (speaking 

 of both Trias and Jura), is subject to question. Until decisive palse- 

 ontological proof may have been obtained, either confirming or refuting 

 the opinion now held and expressed, it is necessary to leave room for 

 doubt as to their true position. Lithologically and geognostically they 

 agree very well throughout Colorado, so that they can be readily recog- 

 nized. Stratigraphically they are almost invariably conformable with 

 older and younger formations, and adapt themselves to the general 

 structure of the region. It is possible that future discoveries may 

 change the views we now hold provisionally with reference to the Jura- 

 Trias, but inasmuch as classification is but the expression of our pres- 

 ent knowledge, it is perfectly justifiable that in geological discussions 

 the groups should be separated. It seems surprising that no paleeonto- 



