I THE PITCH LAKE OF LA BREA. 317 



rm clusters, either completely or partially surrounded by 

 water. 



The centre of the lake — the pitch-pot, or cauldron, as it is 

 called — is at all times so soft, that any person remaining on it 

 would run the risk of sinking, more or less, in the thick sub- 

 stance. There a slow but constant bubbling and puffing is per- 

 ceptible, accompanied by the emissions of gaseous substances, 

 and the throwing up of a yellowish mud, quite cold and of an 

 acrid saltness. Over the entire extent, the degree of hardness 

 varies with the intensity of the solar rays, at early morn the 

 whole surface, excepting at the centre, is hard ; whilst, at mid- 

 day, it becomes so much softened that it retains the stamp of 

 the lightest impress. 



Whenever any quantity of bitumen has been dug and taken 

 up from the lake, the excavation soon fills up, and a perfect level 

 is restored within a short time. The deeper the digging, the 

 quicker the restoration. In the centre trees or branches are 

 sometimes seen emerging to the surface, to be submerged soon 

 afterwards. Casks placed near the spot to receive bitumen have 

 also disappeared. 



It is evident, from the above observations, that the operation 

 going on in the Pitch lake may be ascribed to a revolving 

 motion, a sort of ebullition which continually presses up the 

 asphaltum from the centre to the surface. There is no difficulty 

 in admitting this process, as the mass thus thrown up is semi- 

 fluid, owing to an admixture of an oily substance. It has been 

 noted that the surface of the lake is divided into a number of 

 small bituminous areas, each owing its existence, undoubtedly, 

 to a centre of emission from which the asphaltum has been 

 pressed up. On reaching the surface, it spreads slowly ; the 

 oily substance gradually evaporates on exposure to the direct 

 action of the sun, the outer portion becomes harder and less 

 fluent than the inner, which continues to ascend — to "roll 

 under," as expressed by Mr. Manross — thus giving to the sides 

 of the chasms their curved forms. Messrs. Wall and Sawkins, 

 however, do not admit that explanation ; but they suggest that 

 " when two adjacent masses come in contact, and are not suffi- 

 ciently plastic to unite or join together, they leave a division, 

 which originates the depression in question." 



The Pitch lake is not the only spot where bitumen exists in 



