proceedings: geological society 329 



by the Mesaverde, which is composed of 1500 to 3000 feet of sand- 

 stone, shale, and coal, generally forming two prominent ridges. The 

 lower ridge-forming sandstone of the Mesaverde corresponds to the 

 Parkman sandstone, and its upper ridge-forming sandstone repre- 

 sents the Teapot sandstone of Natrona County. The Parkman and 

 Teapot, with the intervening shaly sandstone, are from 800 to 1500 

 feet thick. The Mesaverde roughly corresponds to the Judith River 

 of Montana and marks the maximum withdrawal of the Montana 

 sea. Succeeding the Mesaverde in Carbon County is from 600 to 

 3000 feet of marine shale (Lewis) and marine sandstone in the base 

 of the Lower Laramie. This marine series above the Mesaverde 

 is equivalent to the 1000 ± feet of marine shale and sandstone in Natrona 

 County between the Teapot sandstone and the Lance. It probably 

 includes within its upper portion beds which are equivalent to the 

 Fox Hills of northeast Wyoming. The Lewis is approximately the 

 time equivalent of the Bearpaw and marks the last great incursion of 

 the Cretaceous sea, which, receding, laid down the Fox Hills sandstone. 

 The upper limit of the marine beds in this area serves as another datum 

 plane. The marine deposits in Carbon County are overlain by 1000 

 to 6000 feet of continental deposits (Lower Laramie), which are iden- 

 tical in Hthologic character, manner of bedding, and topographic ex- 

 pression (moderate ridges) with the 2000 to 3000 feet of Lance beds 

 in Natrona County, which are only 36 miles away. In both there 

 is an entire absence of conglomerate and both have taken part fully 

 in the orogenic movements affecting all the lower formations. The 

 Lance in Natrona and adjacent counties is overlain by 2400 to 4500 

 feet of Fort Union. The Lance and Fort Union are structurally con- 

 formable, as are the Lower Laramie and parts of the Upper Laramie. 

 The peculiar irregularity of structure in the lower Fort Union })eds 

 gives them a rough appearance and they form a pronounced ridge 

 in the topography. They are precisely like the basal part of the Upper 

 Laramie in Carbon County. In both Natrona and Carbon Counties 

 these beds contain cherty conglomerate and at Alkali Butte and at 

 Whiskey Peak in Fremont County they contain fragments of Mowry 

 shale, which is a formation in the Colorado group stratigraphically 

 about 10,000 feet below either the L^pper Laramie or Fort LTnion. 

 The first appearance of these fragments of Mowry in any overlying 

 formation is indicative of important orogenic uplifts, and the signifi- 

 cance of the evidence cannot be disregarded. This lithologic evidence 

 has been interpreted by Veatch to indicate the existence of an uncon- 

 formity between the Lower and Upper Laramie, but the remark- 

 able relations of overlap on older beds inhibited by a part of the Upper 

 Laramie may be interpreted as due to an unconformity within the 

 Upper Laramie. At Alkali Butte in Fremont County the Fort Union 

 is only 250 feet above the marine beds, indicating either an unconform- 

 ity below the Fort L^nion or an extraordinary thinning of the Lance. 

 The unconformity described by Veatch is not stratigraphically at 

 the place of the assumed unconformity at the top of the Fox Hills. 



