The American Museum Journal 



Volume XIII NOVEMBER, 1913 Number 7 



THE ASPHALT GROUP OF FOSSIL 

 SKELETONS 



THE TAR-PITS OF RANCHO-LA-BREA, CALIFORNIA 

 By W. D. Matthew 



THE Museum has just completed and placed on exhibition a group to 

 illustrate one of the most marvelous fossil deposits of the world. 

 This is the famous asphalt formation of Raneho-Ia-Brea near Los 

 Angeles, California. 



The petroleum of southern California, as in most of the West, has an 

 "asphalt base" — that is to say when it evaporates, the heavy oils left 

 behind are asphaltum instead of paraffin. Wherever the petroleum oozes 

 up from the earth in springs, this residuum of asphalt accumulates. The 

 oil wells up continually from below and keeps it soft close around the spring, 

 but elsewhere it is hardened into a solid mass mixed with earth or wind-blown 

 dust. At the Rancho-la-Brea, in the centre of a broad open valley close to 

 the city, is an extensive formation of this sort, made by oil springs which 

 were probably much more active in former times than now. Here and there 

 on the surface are little pools of semi-liquid asphalt, covered with a film of 

 dust in dry weather, with water after a rain, yielding slowly beneath the 

 weight and clutching with unbelievable tenacity whatever sinks beneath 

 the surface. To the inexperienced eye the dust-covered surface looks like 

 firm ground; except in the softer pools one can walk across it without any 

 considerable yielding. But woe to the unfortunate animal that steps into 

 one of the softer pools, or lingers on his way across a firmer surface to look 

 about him or to drink of the water collected over the asphalt surface. His 

 feet sink below the surface, the treacherous tar clutches them fast, and his 

 most desperate struggles result only in sinking him deeper and deeper. 

 Escape is impossible; he succumbs finally to exhaustion and little by little 

 is sucked down and disappears. 



Such has been the fate of many small animals in the last few years. 

 Larger animals too, cattle, horses and dogs have been caught in the asphalt, 

 some dragged out by the aid of ropes, while others not seen in time for rescue, 

 have perished miserably. But the tar-pits although cruelly effective to the 

 limit of their size, are not now large or numerous enough to constitute a 

 serious danger. 



At the time when these springs were active the asphalt pools were muc h 



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