1912] Miller: Pacific Coast Avian Palaeontology 107 



The exact time-relations between the several faunas is not 

 determinate, and the overlap of one column upon another is 

 purposely indefinite. The Equus fauna is considered in part 

 older than the Megalonyx fauna and this in turn than the 

 Ovibos. 



It must be stated also that the study of mammalian remains 

 from Rancho La Brea, from the caves of California, and from 

 Fossil Lake, Oregon, is still being actively pursued and the list 

 of species revised. Any statement of time-relations must be 

 considered as purely tentative. Few investigators have had so 

 wide and so comprehensive an acquaintance with the mammalian 

 palaeontology of North America as has Professor Osborn; hence 

 it is considered in this connection that his chronological arrange- 

 ment of the various mammal-bearing horizons represent the 

 truth as nearly as we have yet arrived at it. 



It will be noted that the Fossil Lake horizon is placed by 

 him midway in the tabulation of the Equus Zone fauna while 

 Rancho La Brea and the caves occupy the middle and upper 

 parts of the Megalonyx Zone. Thus Fossil Lake is to be con- 

 sidered as the earliest Pleistocene horizon on the coast produc- 

 tive of avian remains. 



If we apply the criterion of percentage of extinct forms, 

 the evidence furnished by the avian remains would indicate 

 a different time-relation than that suggested by Professor Os- 

 born. The various horizons here discussed show the following 

 sequence when arranged according to the percentage of Recent 

 species of birds recorded fossil: 



Eancho La Brea 60% still living 



Fossil Lake 66% still living 



Potter Creek Cave 68% still living 



Samwcl Cave 72% still living 



Hawver Cave 79% still living 



The application of this principle in the case of fossil birds 

 seems, however, less accurate than in the case of mammals when 

 we consider the migratory nature of many bird species. The 

 Fossil Lake fauna according to this basis of estimate would 

 appear to be younger than that of Rancho La Brea. A glance 

 at the list of species from Fossil Lake shows, however, the large 



