1912] Miller: Pacific Coast Avian Palaeontology 105 
There is some very eredible 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 aceumula- 
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 fer 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.** 
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.*® 
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, 
39 Osborn, H. F., The Age of Mammals. New York, 1910. 
