310 BRAKSON AXD GREGEE AMSDEX FORMATION OF WYOMING 



Eange, one of which is Pennsylvanian and the other Mississippian, ac- 

 cording to Girty.* Data presented in this paper indicate the homotaxy 

 of the Amsden of the east side of the Wind River Mountains and the 

 Sainte Genevieve of the Mississippi Valley. 



Fossil Horazoxs and Locatioxs 



Several years ago Mr. N. H. Brown, of Lander, Wyoming, called Mr. 

 Branson's attention to some fossils that he had collected in outwash from 

 an irrigation ditch a few miles south of Lander, and in 1911 Branson 

 collected some of these, but could not find from whence they came, though 

 the probable source was the Amsden. In 1913 the fossils were found in 

 place a few miles south of the Little Popo Agie River, in the Wind River 

 Mountains, and collections were made from several localities. In 1916 

 Branson made a small collection in the Bull Lake region northwest of 

 Lander and further collections in the Little Popo Agie region. 



The fossilization differs sharply in different regions. Near Bull Lake 

 the fossils are of calcite and poorly preserved; at one place south of the 

 Little Popo Agie they are all silicified and the silica is often highly col- 

 ored, while three miles from the silicified fossils the preservation is mainly 

 in hematite. 



In the Popo Agie region the exact horizon of the fossils was not deter- 

 mined, as both the top and bottom of the formation are covered. Good 

 exposures of the Amsden seem to be absent from the southern Wind River 

 Mountains, and at the best the outcrops consist of a few feet of rock in 

 place. In section 19, township 31 north, range 99 west, about four miles 

 south of the Little Popo Agie canyon, more than three feet of sandy, 

 highly ferruginous shales outcrop about 60 feet from the base of the for- 

 mation. In places these shales grade into a concretionary iron ore, and 

 fossils occur above them and probably in and below them. Alcove they 

 are in a yellow, impure limestone, and in a red to purple impure lime- 

 stone. The purple limestone was not found in place, but in the float in 

 the same locality as the red shales. The fossils occur weathered out on 

 the slopes for about 20 feet above the shales. 



Sectiox axd Descriptiox of the Amsdex 



There are exposures of the entire formation in vertical cliff's in the Bull 

 Lake region. The iron, sandstone, and shales of the Popo Agie region do 

 not appear and the rock is mainly dolomite and limestone. The followino- 



Am. .Tour. Sci.. vol. 87, 4th ser., pp. 175-176. 



