THE EVIDENCE OF THE WYOMING CONGLOMERATE. 251 



•region with the views of either Powell or Dutton, with regard to the deter- 

 mination of the course of the Colorado river ; and I am inclined to think that 

 future investigation will prove that they have placed it at too early a date. 

 I have already shown * that the Wyoming conglomerate (Bishop Mountain 

 conglomerate of Powell), which has escaped erosion along the flanks of the 

 Uinta mountains, is so situated as to prove that it must once have extended 

 over the entire eastern end of the mountaius through which the canon of 

 the Green river is now cut, forming a nearly level surface at an altitude 

 corresponding to a present elevation of between 9,000 and 10,000 feet, and 

 that the river must have initiated its present meandering course over this 

 surface as a superimposed valley. This conglomerate is considered by all 

 who have examined the region to be of very late age, either Pliocene or 

 Quaternary, though no fossils have yet been found in it. It is everywhere 

 horizontal and undisturbed, showing no stratification planes, but at one 

 exposure shows a thickness of 200 feet of rounded pebbles derived from the 

 Uinta quartzite, cemented iuto hard rock by an abundant lime cement. The 

 situation of its remaining exposures is such that I cannot conceive of the 

 possibility of the existence of the canon of the Green river during its 

 formation. While in the Plateau province south of the Uinta mountains no 

 beds have yet been discovered that are known to be of later than Eocene 

 age, the region has not yet been examined with sufficient detail to make it 

 certain that they have not existed there. Such beds would have been the 

 first to be affected by the enormous erosion to which the entire region has 

 been subjected, and the present limited extent of the Wyoming conglomerate 

 (which has doubtless been exceptionally protected by its position along the 

 flanks of the range), as compared with that it must once have had, proves 

 how thoroughly such recent deposits could have been carried away by recent 

 erosion. 



In more recent observations in northern New Mexico,f Captain Duttou 

 found upper Carboniferous beds resting directly on the Archaean in theZuni 

 plateau and the Nacimiento mouutains, the Cambriau, Silurian, and De- 

 vonian being wanting. 



In more detailed studies of previously examined sections in the Grand 

 Canon of the Colorado, Mr. C. D. Walcott J has recoguized a great thickness 

 of comparatively unaltered saudstones, shales, and limestones (the Chuar and 

 Grand Canon series), which he considers of Algonkian age, and which rest 

 unconformably upon sandstones and eruptive granites of undetermined age. 

 A distinct unconformity of angle exists between the Algonkian and upper 



* Descriptive Geology: Vol. II, Fortieth Parallel reports. Washington, 1887, pp. 194 and 205 (field 

 work, 1871). 



t Mount Taylor and the Zufii Plateau : Cth Ann. Rep. Director U. S. Geol. Survey. Washington, 

 1885, p. 132 (field work, 1881). 



t Am. Jour. Sei., 3d ser., vol. XX. p. 221 ; vol. XXVI, p. 437; vol. XXVIII. p. «1 ; vol. XXX I 1, p. 

 154; vol. XXXV. p. :i'M ; vol. XXXVII, p. 374; vol. XXXVIII, p. 2'J ; and Bull. U. S. Geol. Survey, 

 No. 30, 1886, p. 15. 



