1916] Merriam-Stock— Moody : An American Pliocene Bear 



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lation of the Rattlesnake. On the other side this stage is limited by 

 the date of subsequent Pleistocene terraces and the period of canyon 

 cutting intervening between the close of the Rattlesnake and begin- 

 ning accumulation of the terrace deposits. 



The known mammalian fauna of the Rattlesnake comprises between 

 twenty and thirty species. The available representation will be fully 

 discussed in an early publication. The horses are presumably the 

 most important elements of the fauna for purposes of palaeontologic 

 and geologic correlation. The Equidae are represented by species of 

 the Hipparion and Pliohippus groups having their nearest relatives 

 in beds referred to the early Pliocene of the Great Basin and Pacific 

 Coast provinces. The view that the Rattlesnake fauna is related to 

 that of the Thousand Creek Pliocene in Nevada receives support 

 through the discovery of a horn-core of the peculiar antelope 

 Sphenophalos in the Rattlesnake, in the course of the past season's 

 work. This antelope has heretofore been known only from the 

 Thousand Creek, where it occurs in association with twisted-horn 

 antelopes of the Ilingoceros type. 



In the locality at which the bear remains were found the Rattle- 

 snake formation consists principally of a series of cross-bedded gravels 

 alternating with varicolored tuffs and sands. A persistent rhyolite 

 flow occurs at a high horizon in the formation. Pebbles in any single 

 stratum are usually of comparable dimensions, but sharp changes occur 

 in passing from one bed to another. Thus a stratum with bowlders 

 attaining a diameter of one foot may immediately overlie a bed in 

 which the largest pebbles have a diameter of not more than one-half 

 inch. It was in a layer of the finer gravel that the bear remains were 

 discovered. The bed seems to be lenticular, but this appearance may 

 be due to occurrence of the gravels on the summit of a ridge. Maseall 

 Miocene is exposed in the bed of Rattlesnake Creek to the north of 

 the ridge upon which the gravels were found. This ridge has an 

 approximate elevation of 150 feet above the level of the stream, 

 thus placing the horizon at which the bear remains occurred well up 

 in the Rattlesnake section. The erosion of Rattlesnake and Little 

 Rattlesnake creeks has removed a large part of the formation south 

 of the course of the former stream, and the section is known to be 

 thicker toward the south. It has therefore not been found possible 

 to ascertain the exact distance below the summit of the section repre- 

 sented by the bed in which the bear specimen was found. This horizon 

 is believed to be stratigraphically within the limits of about 100 feet 



