18 BUREAU OF AMERICAN ETHNOLOGY [bull. 66 



the excavators obtained iiU possible information as to the nature of the deposit 

 in which the specimen was found, and every bone appearing in the deposit was 

 saved. The final results of the work give us a complete map of the deposit 

 and full list of the animal remains from the two chimneys, with their situa- 

 tion in the chimneys. 



******* 



Purely geologic evidences of age are often exceedingly difficult to obtain in 

 asphalt deposits, owing to the peculiar mode of accumulation, and the possi- 

 bility of movement in the deposits after they are once formed. The asphalt is 

 a residue from evaporation of oil. It accumulates either on the surface of the 

 ground or in the midst of other strata into wh'ch it has soaked or poured. 

 Even after the asphalt deposit has formed, the nature of the vi.scous material 

 makes possible considerable movement in many directions within the mass 

 and consequent change of position of any materials in it. 



The deposits in which fossil remains have been found at Rancho La Brea 

 are evidently in part layers formed on the surface, and in part pipes, pockets, 

 and chimneys through which oil came up from deeply buried strata. The 

 source of the asphalt or o'l is a deep-lying formation, which is considerably 

 folded, and is covered by approximately horizontal layers of clayey and sandy 

 strata washed in from higher land not far away. Oil and gas have been seeping 

 through the superficial horizontal deposit for a very long period, and have 

 formed more or less definite channels or pipes along lines of least resistance. 

 In some cases these pipes have evidently enlarged themselves locally to chim- 

 neys several feet in diameter. 



At pit No. 10, in which the human remains were discovered, the asphalt de- 

 posit consists of two pipes or chimneys connecting with surface flows above. 

 The chimneys arise below from a large dome-shaped asphaltic reservoir. This 

 dome may be an old surface pool now buried and forming a part of the pas- 

 sageway for further upward movement of oil ; or it may be an enlargement of 

 a chinuiey that was originally very much smaller. 



The asphalt in the chimneys and in the dome in pit 10 was largely a soft, 

 viscous mass containing a high percentage of sand, and including in some re- 

 gions many angular lumps of hard, weathered asphalt. The contents of the 

 chimneys are entirely unlike the surrounding soil or rock. The material 

 through which the chimneys pass is not homogeneous, but is composed of ap- 

 proximately horizontal strata of clay, sand, and gravel, with a small inclusion 

 of asphaltic material in most places. The contact between the chimneys and 

 the matrix through which they pass was everywhere sharply marked. 



* * * , * * * * 



Bones of birds and mammals were abundant in both chimneys. In the 

 south chimney, which is wide above and narrows sharply below, large bones 

 are found only above the narrowing of the pipe. In the large reservoir below 

 the chimneys only small bones appear, and these were found only in a limited 

 space near the point of union of the lower reservoir and the two chimneys. 

 The distribution of bones shows conclusively that they came from above, and 

 were not carried up from the depths with ascending oil. 



The total number of specimens found in the chimneys was large, and will 

 aggregate several thousand. These bones represent a considerable variety of 

 mammals and birds. They include bear, coyote, a wolf of the timber-wolf type, 

 skunk, weasel, horse, antelope, rabbit, pocket gophers, field nnce, eagles, owls, 

 ^ultures, crows, and many other forms. 



The fauna from the two chimneys in pit 10 Is in general like that of Cali- 

 fornia at the present time. It differs greatly from that of the pits in which 



