July, 1922 FOSSIL BIRDS FROM McKITTRICK 125 
constituted the Pleistocene environment that attracted them. Whether subject 
to complete periodic obliteration or not, it probably did fluctuate greatly in ex- 
tent within its shallow basin. The fossil remains are-found sparsely distributed 
over a wide area and preserved in the silt-like accumulation at the bottom of the 
ancient lake. There is no evidence of concentration at one point such as appears 
at both the asphalt horizons. It hardly seems credible that waders were lacking 
at Fossil Lake or that gulls and divers shunned the neighborhood of McKittrick 
during Pleistocene time. The difference between the two avifaunas is more prob- 
ably due to difference in method of entombment rather than to diversity of phy- 
siographic or of climatic environment. Probably the birds actually present dur- 
ing the Pleistocene were much the same in the two localities, although it is likely 
that there was more marsh and slough country in the neighborhood of McKitt- 
rick. | 
On the other hand, the differences between the McKittrick and the Rancho 
La Brea collections are due probably to an actual difference in fauna due to 
diversity of the immediate environments of two localities in which the method 
of entombment was the same. 
Regarding the particular part of the Pleistocene to which the McKittrick 
assemblage belongs, it is too early yet to comment at anv length. The writer 
has already pointed out (Univ. Calif. Publ., Bull. Dept. Geol., vol. 7, no. 5, 1912, 
p. 105) the inaccuracy of avian remains. as indices to the relative age of two 
faunas where one of them includes a much larger proportion of migratory spe- 
cies than does the other. Just such diversity of habit sets off the McKittrick 
assemblage from that of Rancho La Brea. This fact eouvled with the povertv 
of material thus far excavated from the former beds makes comment upon their 
relative ages at present inadvisable. Both seem, however, to have been accum- 
ulated during a time when the climate was warmer than at present, though 
whether or not during the same Pleistocene amelioration can not be stated. 
Los Angeles, California, May 15, 1922. 
