Vol. 5] 



Merriam-Sinclair. — Tert iary Fa unas. 



175 



formity is the Mascall formation. The lower beds, from which 

 numerous leaf impressions and poorly preserved fish remains 

 have been obtained, are described by Calkins as fine-grained, 

 chalky rocks, probably in part of organic origin. Grey friable 

 tuffs composed largely of glass particles also form part of the 

 series. The upper beds which yield the mammalian remains are 

 tuffs of light color, fine grain, and harsh texture. At several 

 localities thin basalt flows are interstratified with the lower 

 Mascall beds. 



Upon the uptilted and eroded edges of the Mascall there 

 lies a considerable thickness of gravel, tuff and rhyolitic lava 

 which has been named the Rattlesnake formation, from its 

 typical occurrence on Rattlesnake Creek near Cottonwood. The 

 basal gravels of the Rattlesnake contain many pebbles evidently 

 derived from the Columbia Lava. Vertebrate remains have 

 been obtained from both the tuffs and the gravels. 



The tuffaceous layers are irregularly bedded but appear to 

 have been worked over by wind, and to have formed soil or dirt 

 beds supporting a considerable growth of plants. In some 

 places the.y are filled with slender cord-like bodies which evi- 

 dently represent mineral accumulation about small roots. Along" 

 one section of a soil bed a large number of fragments of horse 

 bones and teeth, evidently all belonging to one individual, were 

 scattered for a horizontal distance of ever twenty feet and 

 through one and one-half feet in thickness. The scattered and 

 broken condition of the bones of this individual seem to indicate 

 a long exposure of the remains on a land surface which was. 

 being rapidly worked over. 



In some sections the prominent rhyolitic bed forms the cap 

 of extensive tables. In other regions, as near Belshaw's ranch, 

 there are at least two hundred feet of gravels above the rhyolite 

 bed. 



The close of Rattlesnake deposition marks the beginning of 

 an interval of erosion which may be regarded as the opening 

 event of the Quaternary. It has been suggested that the 

 deformation of the Rattlesnake occurred after the John Day- 

 River had established itself in its present course. 8 



6 Merriam. Op. ait., p. 312. 



