22 



THE POPULAR SCIENCE MONTHLY 



Photo, C. R. Toothaker, Phila. Commercial Museum. 

 Soft Asphalt Rising through Water. 



The surface of the deposit or lake is not a uniform expanse of pitch. 

 It is grassy along the edges and becomes free from vegetation at some 

 distance from the center. Shrubs and small trees occur in a few 

 cases known as islands. These patches move from place to place with 

 the movement of the pitch at the surface. The main mass of asphalt is a 

 broad expanse of pitch made up of separate areas of irregular outline, but 

 at times quite circular, which are separated by channels, filled with rain 

 water, which prevents their coalescence. The boundaries are depressed 

 and the center of the areas is always somewhat elevated above the 

 edges, that is to say, they are mushroom-like. The origin of the separate 

 areas evidently lies in the constant movement of the crude material, due 



Photo, C. R. Toothaker, Phila. Commercial Museum. 

 Evolution of Gas in Water. 



