STATE OF PRESERVATION AND QUANTITY OF FOSSIL REMAINS 



The skeletal remains obtained at Rancho La Brea vary greatly in the state 

 of preservation at different horizons and at different places in the same bed, 

 but in all cases the material seems to be the practically unaltered bone. In 

 most localities the bones are fairly hard and are easily extracted from the 

 matrix. In other places they are very soft and can be removed only with great 

 difficulty. At still other points the enclosing asphalt is very hard and has the 

 appearance of having been exposed to the sun and to weathering action for a 

 long period. In these portions of the beds the bones can be separated satisfac- 

 torily only with the aid of chisel and mallet. 



As the greater number of the annuals entombed in the Rancho La Brea 

 Beds have been entrapped in the tar, it is to be presumed that in a large per- 

 centage of cases the major portion of the skeleton has been preserved. Con- 

 trary to expectation, connected skeletons are not common. Several factors have 

 evidently combined to scatter the skeletal parts. In most localities the tangled 

 mass of bones shows that the tar at these points remained for a long period 

 soft enough to engulf the bodies of animals, and during this time the struggles 

 of each new victim tended to disturb the skeletons already in the pool. At 

 times when the surface of the asphalt hardened by exposure, such bones as 

 were uncovered may have been broken or perhaps completely destroyed by 

 ungulates tramping over the spot. At all periods during the history of the 

 deposit the viscosity of the asphalt apparently permitted considerable move- 

 ments in the mass, and the individual bones were moved apart in the viscous 

 layers. These movements would continue after the asphalt beds had been 

 deeply buried by later accumulation, as the pressure of the mass above would 

 at times cause a certain degree of flow in the tar beds. 



The pressure of the rock mass does not seem in general to have distorted 

 the bones greatly. Even the skulls of large animals commonly show compar- 

 atively little flattening or twisting. "Where one bone has come to rest directly 

 against another, the weaker or softer one is sometimes dented by the harder 

 one ; but where the pressure has been exerted through the asphalt above there 

 has usually beeu change of position rather than change of form. 



Judging by the results of excavations carried on up to the present time, the 

 quantity of animal remains entombed in the beds at Rancho La Brea is large. 

 The total area of asphalt in the region, including all of the small outcrops, prob- 

 ably amounts to the larger part of a square mile. A considerable part of this 

 area presumably contains few hones, but fragments are present in a large 



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