392 University of California Publications in Geology [Vol. 7 



GENERAL CONCLUSIONS AS TO THE MODE OE ACCUMULATION 

 AT THE LOCALITIES IN VESTIGATED 



The most interesting observation on the deposition of material 

 found in the recent excavations in the asphalt is that bones 

 accumulated in holes of such small size, and that the deposits 

 were built up to such a thickness. As seen in the section in 

 plate 21, the maximum depth of one pocket is at least twenty- 

 three feet, while the area over which it extends is comparatively 

 small. These pockets were not at any time depressions, twenty 

 to twenty-five feet deep in the Pleistocene surface, which later 

 filled up gradually with sand, clay and bones. From the presence 

 of green clay dividing pockets no. 1 and no. 2 (plate 20) it may 

 look as though they were rilled up in this manner, but it is 

 obviously impossible for this wall of clay between the pockets 

 to have resisted ordinary rain erosion during the time in which 

 the pockets could receive by any natural process the enormous 

 mass of bones found in them. It seems quite certain that these 

 deposits were slowly built up along with the surrounding Pleis- 

 tocene formation, and that the tar pools were constantly renewing 

 their surfaces as the tar came out and trapped the life of that 

 time. Locality 2051 affords the best example of this manner of 

 deposition, as at this point three distinct pockets were found 

 in a space of sixty feet. Through all the years that must have 

 been required for the building up of these asphalt masses the 

 exudation of the tar was so slow that the pools never joined to 

 form a large pool and a single large mass of bones, but remained 

 distinct. However slow the accumulation of the bones was, the 

 pools were evidently large enough to catch one or two tigers, 

 several wolves and an ungulate at the same time, the latter serv- 

 ing as prey for the carnivores. This association is quite clearly 

 shown in some places, and at one point in particular there were 

 eight wolf skulls and many wolf bones mixed with the bones and 

 skull of a large bison. 



In all the localities investigated the quantity of bones ob- 

 tained was very large compared with the amount of asphalt 

 removed. Each pocket represented a mass of tangled bones so 

 closely matted that when one bone was removed there was always 

 another exposed. Soon after the animals were caught in the 



