OCCURRENCE OF THE FOSSILS 



551 



the Bighorn mountains. They were also found to occur at frequent in- 

 tervals southward for the next 7 miles to the southern margin of the Big- 

 horn formation, which is on the headwaters of another branch of Powder 

 river, 15 miles northwest of Barnum post-office, in the southeastern por- 

 tion of Bighorn county. 



The relations at the locality first mentioned above are shown in the 

 following section : 



B, MADISON LIMESTONE 



BIGHORN LIMESTONE 

 s^lJJH BEARING SANDSTONE 



OWOOD FORMATION 



Figure 3. — Cross-section of Butte near Summit of Bighorn Mountains, 23 Miles West of 



Mayo worth, . Wyoming. 



The sandstone at this locality is from 6 to 8 feet thick, and it outcrops 

 frequently. It is moderately coarse grained, varies from hard to soft, is 

 massive, and in part shows considerable cross-bedding. Its color varies 

 from dirty buff to light gray, and many of the weathered portions are 

 brownish. Some portions appear oolitic, owing to concretionary growth of 

 the sand grains. The contacts above and below are sharp, but with no 

 marked evidence of unconformity. The underlying beds are Deadwood 

 limestones and shales, the former containing flat pebble conglomerate of 

 intraformational type. A short distance below the contact fossils occur, 

 consisting mainly of Dicellamus politus in large numbers and a few 

 trilobite fragments, apparently Ptychoparia owenii, which are characteris- 

 tic of the Middle Cambrian. The overlying massive limestone is typical 

 Bighorn limestone, containing occasional maclurinas and corals. There 

 can be no question as to the stratigraphic position of the fish-bearing sand- 

 stone below this limestone, for the superposition is plainly exposed here 

 as well as at many localities northward. The Bighorn limestone is here 

 only about 40 feet thick, or one-eighth its thickness in its maximum de- 

 velopment in the northern portion of the Bighorn uplift. As explained 

 above, the diminished thickness apparently is due somewhat to thinning 

 of the original deposit, but mainly to the absence of the upper portion 

 removed by erosion prior to Carboniferous time. The overlying Madison 



