286 PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 83 



able portions of the formation are noticeably gypsiferous, indicating 

 periods of desiccation. 



EVIDENCE AS TO AGE OF BEDS 



The Idaho formation was early believed by Cope to be Pliocene on 

 the basis of the fish remains that he described from these beds, and 

 subsequent small collections of land vertebrates from various localities 

 for the most part probably mthin the Idaho formation were considered 

 as Pliocene by Leidy, Lucas, and Marsh. Merriam,'^ in 1917, reviewed 

 the vertebrate evidence for the Pliocene age of various deposits in the 

 Pacific coast and Great Basin regions and concluded for the Idaho beds 

 that they were late Pliocene verging on Pleistocene, More recently 

 Hay^^ expressed the opinion that the Idaho beds were Nebraskan in age. 

 His reasons for considering them Pleistocene were unfortunately based 

 primarily on materials coming from the river gravels in the eastern 

 portion of the Snake River Basin, which are apparently no part of the 

 Idaho formation. 



The Plagerman lake beds, which may be considered a part of the 

 Idaho formation, have produced a fauna that is probably an associ- 

 ated assemblage. Wliether these forms were contemporaneous with 

 those described from localities farther west believed to be within the 

 Idaho formation there may be some doubt. It is my opinion that 

 if these faunas are of different age the Hagerman assemblage may be 

 slightly older than those at Bruneau River, Castle Butte near Grand 

 Yiew, Sinker Creek, and scattered occurrences in the Nampa-Caldwell 

 region not coming from the Payette or Ironsides horizons. This 

 opinion is based on the difference between certain of the Mammalia 

 occurring at Hagerman and similar forms found elsewhere in the 

 formation. Moreover, the fish assemblage seems not to include 

 several of the large types abundantly represented in the more typical 

 Idaho beds. 



The Mammalia found at Hagerman appear to be in an advanced 

 Pliocene stage both in development of several of the forms represented 

 and in the composition of the fauna. Most noticeable is the absence 

 of forms typically Pleistocene in age, as mylodont sloths, mammoths, 

 Mastodon americanus, true Equus, bison, musk-ox, Ursus, Castoroides, 

 and Lepus. Most of these are recognized in early or lower Pleistocene, 

 possibly Aftonian, as indicated by Calvin's ^* work, or Yarmouth 



12 Merriam, J. C, Univ. California Publ. BuH. Dept. Qeol., vol. 10, no. 22, pp. 421-443, 1917. 

 " Hay, O. P., Carnegie Inst. Washington Publ. no. 322B, p. 269, 1927. 



14 Calvin, Samuel, Bull. Oeol. See. Amer., vol. 20, pp. 341-356, pis. 16-27, 1909; vol. 22, pp. 207-216, pis. 

 18-24, 1911. 



