168 PROCEEDINGS OF THE ALBANY MEETING 



AGE AND ORIGIN OF THE RED BEDS OF SOUTHEASTERN WYOMING 

 BY S. H. KNIGHT^ 



(Ahstract) 



The object of this paper is to set forth some recently acquired data which 

 throws additional light on the age and origin of the red beds as they are 

 developed along the eastern base of the Rocky Mountain Front Range, espe- 

 cially along its northern portions. Evidence of both a paleontologic and strati- 

 graphic nature supports the assigning of the greater portion of the Chugwater 

 formation to the Permocarbonic age. It is now known, especially throughout 

 the Laramie Plains region, that the upper 250 feet of the Chugwater is sep- 

 arated from the underlying portion by a disconformity. and that the portion 

 lying above the break is equivalent to the Dolores formation of southwestern 

 Colorado. The evidence for correlating this upper 250 feet, which has been 

 assigned to the Chugwater, with the Dolores, lies in the presence of a pebble 

 conglomerate composed of small limestone pellets, wood fragments, and frag- 

 mentary remains of Triassic vertebrates. This peculiar conglomerate is identi- 

 cal in its lithological and stratigraphical habit with the typical Dolores con- 

 glomerate, and it contains similar fragmentary remains. 



From the foregoing it is evident that in the northern portion of the Rocky 

 Mountain Front Range the dividing line between the Paleozoic and Mesozoic 

 lies within 250 feet of the top of what has previously been held as Chugwater 

 formation. Owing to the widely different age relationship between the upper 

 and lower portions, as manifest by the difference in the fossil content, I would 

 suggest that the name Chugwater be limited to that portion of the formation 

 which is Permocarbonic in age, and that the upper 250 feet be separated as a 

 distinct formation, to be known as the Jelm formation, from the good exposures 

 of the characteristic bone-bearing conglomerate near the east base of Jelm 

 Mountain. 



Evidence in proof of the continental origin of this complex group of sedi- 

 ments is fast accumulating. Numerous field observations now at hand await 

 detailed laboratory study before the problem can be satisfactorily solved. 



Presented in abstract extemporaneously. 



Discussion 



Prof. Erasmus Haworth : I would like to ask the author if he considers 

 the cross-bedding shown on the canvass as positive evidence that such forma- 

 tions must have been accumulated and arranged by eolian processes? In the 

 Pennsylvanian of Kansas and some parts of Missouri we have a limestone bed 

 with as plainly marked cross-bedding as those shown. This limestone has 

 massive fossils and is interbedded with other limestones and shales, always 

 considered of massive origin. 



Prof. E. B. Branson : On the eastern slope of the Wind River Mountains 

 the Chugwater is about 1,500 feet thick and there is a well marked uncon- 

 formity about tlie middle. The Popo Agie beds, 60 to 80 feet thick, which are 



1 Introduced by A. W. Grabau. 



