Dahe — Episodes in Rocky Mountain Orogeny. 253 



Basin. This then forces ns to one of three conclusions. 

 Either (1) the first phase of the Rocky Mountain folding 

 in Colorado is actually earlier than any of those described 

 in Wyoming, being actually pre-Lance while they are post- 

 Lance; or (2) the Arapahoe is not the true equivalent of 

 the Lance of the type locality; or else (3) the so-called 

 Lance of the Big Horn Basin is not the exact equivalent of 

 the original Lance. The writer has been unable to find the 

 necessary data for a solution of this threefold possibility. 

 We should probably hesitate before postulating another 

 period of folding in Eocky Mountain orogeny, especially 

 in view of the uncertain state of the Fort Union-Lance- 

 Laramie correlation. There are those who believe that 

 diastrophic e^ddence will be the final criterion in settling 

 this problem. It is admitted that diastrophism is a valua- 

 ble aid in correlation, but before it can be used in settling 

 this problem, we must know quite beyond doubt whether 

 or not there are more than three episodes in the orogeny 

 of the Rocky Mountains, and unless evidences of a fourth 

 can be found in the same restricted area where the three 

 have already been proved, it seems to the writer that to 

 make a final determination must rest on other methods of 

 correlating the strata involved, across \vide intervening 

 areas. 



In this connection it is pertinent to inquire into the 

 relations of the Lance to the underlying beds in the type 

 area and in the Big Horn Basin, to discover whether there 

 is at its base any break comparable to that reported below 

 the base of the Arapahoe beds of Colorado. 



Wegemann,-^ in the Powder River Basin of eastern 

 Wyoming, described the Lance formation as carrying a 

 few thin coal seams and many notable concretions, and as 

 being without evidences of unconformity at either base or 

 top, but describes unconformity between the Fort Union 

 and Wasatch. 



According to Knowlton,^^ in Carbon County, Wyoming, 

 the ''upper Laramie '^ (Lance) rests on the lower Laramie 

 with ''distinct change in the dip, apparently a slight 

 change in the strike, and a marked change in the lithology 

 between the lower and upper beds. " " Not only are the 

 beds * * * above more than 6000 feet of 'Laramie' rocks 



28 Wegemann, C. H. ; loc. cit. 



2^ Knowlton, F. H. ; Further Data on the Stratigraphic Position of the 

 Lance Formation (Ceratops Beds), Jour. Geol., 19, pp. 358-376, 1911. 



