of Albertite and allied minerals. 365 
are only the residue ? 
Is the hypothesis of their derivation from petroleum more 
acceptable, if it be admitted that the substance entered the 
fissure in a semi-solid condition ? The fissure opened and was 
filled. The filling could not be gradual by infiltration, else 
the same questions arise respecting the wall rock and the 
“horses.” The oxydation must then have been completed at 
a depth of more than a thousand feet below the surface. 
Through what agency could the oxydation have been effected 
at that depth ? In California, petroleums were found changed 
by oxydation at a depth of nearly five hundred feet; the change 
however was only slight; they were still fuids. The strata 
too, in that region are very much broken and porous, wherever 
the oils are oxydized beneath the surface. If the veins were 
filled by a residue from the evaporation of petroleum, the 
evaporation must have taken place at a great depth by internal 
heat—certainly not by the sun’s rays. What then became of 
the lighter portion, amounting to from ninety to ninety-five 
per cent? Did the formation contain fissures into which the 
a and New York such veins are remote fro1 
Springs of petroleum, and are usually, if not always, found in 
product in a system of fractional condensation. Distillation 
commences ; if the cavity were hermetically sealed, enormous 
pressure is generated, and a corresponding increase of tempera- 
ture required for further distillation. The pressure increases 
until the crust of the earth is ruptured, and from ninety to 
hinety-five per cent escapes as vapor, leaving a perfectly homo- 
geneous mass which is forced by the collapse into the fissure, 
