SUPPOSED JURA-TRIAS OF THE FRONT RANGE OF, COLORADO. 493 



to deal with the uncertainty than I, and perhaps be the starting point of arriving 

 at a definite enough knowledge to settle the matter. 



In -'Hayden's Geological Report of Colorado, 1876, p. 107," in reviewing 

 -his labors of previous years, he says : " All along the Front Range the Triassic 

 "beds occupy prominent similar positions, until toward the south, they no 

 "longer appear; west of the Front Range they also occur, but not so continu- 

 " ous as at the locality first mentioned. It appears that at but very few places 

 *' the Triassic waters could extend westward of the main axis of the Front Range, 

 "but they found ingress at other points. In their lithological character the strata 

 " of the Triassic formations are very constant; so thoroughly complete is this 

 " constancy that it is no exaggeration to say that the formation can readily berec- 

 '" ognized at a glance." 



In "Dana's Geology, p. 406," occurs the following; "There is still some 

 " doubt as to the age of the beds of the Rocky Mountains referred to the Triassic 

 "period. Although very widely distributed over the eastern slope south of the 

 •*' parallel of 38°, they seldom contain fossils; and the few found — occasional 

 "*' pieces of fossil woods — are not sufficient to settle the question," 



In a foot-note, page 447, " Leconte's Elements of Geology," is stated, " In 

 "^'Colorado, in strata referred by Marsh to the Wealden or uppermost Jurassic, 

 "but by Cope to the lower Cretaceous, a number of immense Dinosaurs have 

 "recently been found; also, by Marsh a small marsupial mammal allied to the 

 " opossum, and about the size of a weasel, which he calls Dyatestes piscus." 



Now we will go a little farther east and take the Dakota, Red Sandstone, 

 f(No. I of the Cretaceous Group), horizon from the Platte River in Nebraska, 

 south through Kansas to the Arkansas River. Throughout this section in a near- 

 hf north and south line, it is resting the whole length on the last sedimentary 

 rocks from the east, viz. the Permian. It must here be noted that the Permo- 

 carboniferous sediments were derived, in a measure, from the wearing away of 

 exposed strata to the east ; while the Dakota sandstone sediments came from the 

 west ; and here two geological sections meet ; each having its own types and pe- 

 culiarities. 



Nowhere can I find it recorded that any Jurassic, or Triassic strata appear 

 between these two rivers, to the east of the Colorado State-line, but throughout 

 the Jura-Trias is entirely wanting, and the sandstone of the Cretaceous rests on 

 the Permian rocks, and I believe conformably to them also ; and these are the 

 last of the series of the old Carboniferous group of the east. 



Now if there was no cause in existence to produce a deposition of Jura-Trias 

 along this horizon, there certainly was no cause to produce it between the same 

 latitudes farther west and have it show, as claimed it does, uptilted along the 

 Front Range of Colorado. 



True, it is mentioned in many places in the U. S. Geological Survey of the 

 State, that the supposed Jurassic and Triassic strata rest upon Carboniferous 

 rocks, and show conformability therewith ; so they do, but the coals below them 

 are the coal-beds of the Cretaceous^ and not the known coals of the Carboniferous 



