368 S. F. Peckham on the probable origin 
unaltered, is no procf that they are unaltered at the point at 
which the bitumen originated. 
Prof. Wurtz mentions two facts as observed in connection 
with the Grahmite, which renders the supposition impossible, 
that the fissure was ever filled with a liquid. They are, first, 
the occurrence of “ horses,” and second, the fact that the porous 
wall-rock of sandstone is not penetrated by the bitumen. The 
occurence of “horses” is equally conclusive proof that the in- 
jection did not take place into a previously formed fissure. The 
determination of the cause which produced the fissure is not 
essential : its position in reference to the subterranean pool o 
melted bitumen was no doubt determined by the pressure ex- 
erted by compressed gaseous hydrocarbons, which accompanied 
the melted mass. The injection was no doubt caused by the 
collapse of the subterranean chamber, and partial expulsion of 
its contents. 
high water, the sand of the shelving beach beneath it, covering 
the upturned edges of the oil shales, but a few feet in depth. 
necting them with the shales below. The largest vein stands 
perpendicularly and at right angles with the face of the bluff. 
It cuts the bluff from the base to the summit, and is wed 
* Rep. Geol. Surv. Cal., Geol. I, 132. 
a a i 
