1912] Miller: Pacific Coast Avian Palaeontology 105 



There is some very credible evidence that the mammals en- 

 trapped in the asphalt pools were in part attracted to the locality 

 by water. Over the top of the asphalt layer there may accumu- 

 late after a shower a stratum of fairly pure rain water, so little 

 does the viscid asphalt mix with the water. Such an accumula- 

 tion remains in the impervious basins until evaporated by the 

 heat of the sun, without loss by seepage through the oil-impreg- 

 nated earth. Pools of water suitable for the use of cattle and 

 horses thus remain impounded in natural reservoirs after adja- 

 cent streams have vanished. Natural reservoirs are of such im- 

 portance in the southwestern deserts as to have received the local 

 Spanish name of "tinajas, " and wild mammals of the desert 

 come from long distances to drink at them. Such conditions 

 would tend to concentrate the remains of mammals of a poorly 

 watered region and furnish the asphalt trap with scores of 

 victims which otherwise would have escaped. 38 



Summing up the evidence of a warm, moist climate during 

 the Pleistocene, we have the following points, all of which are 

 inconclusive : 



1. The presence of species whose nearest relatives are at 

 present more tropical in distribution. 



2. The presence of an abundant fauna which is suggestive 

 of favorable conditions of climate. 



3. The presence of aquatic species and of waterworn chips 

 laid down in places now dry but showing no great changes in 

 topography. 



4. The suggestion that the mammals of Rancho La Brea were 

 in some measure led to the region by the presence of water. 



Time Relations as Suggested by a Study of Bird Remains. — 

 Osborn divides the Pleistocene period into three great time 

 subdivisions, namely, Pre-Glacial, Glacial and Post-Glacial. 30 

 The Glacial again shows evidence of division into five periods 

 of fluctuation, during which the ice cap oscillated northward 

 and southward with the changing isotherms. The period also 

 represents a time of high elevation of the land surface in general 



38 See Darwin, C, Journal of Voyage of H.M.S. Beagle, 1845 (New 

 ed. 1909), pp. 128-130. 



so Osborn, H. F., The Age of Mammals. New York, 1910. 



