of the accumulations about them of the products of the evaporation and
oxidation of petroleum to tar or asphalt. Certain less common oils yield
ozokerite as a solid, and considerable accumulations of this are known
in Galicia and Utah.

Natural paraffine is less abundant, and yet in places it occurs in
considerable quantity. Asphalt is the common name for the solid residue
from the evaporation and oxidation of petroleum; and large accumulations
of this substance are known in many parts of the world, perhaps the most
noted of all being that of the "Pitch Lake". of the Island of Trinidad;
there, as everywhere else, the derivation of asphalt from petroleum is
obvious, and traceable in all stages. The asphalts, then, have a common
history in this, that they are produced by the evaporation and oxidation
of petroleum. But it should also be said that they share the diversity
of character of petroleums, and the term asphalt represents a group of
substances of which the physical characters and chemical composition
differ greatly in virtue of their derivation, and also differ from
changes which they are constantly undergoing. Thus at the Pitch Lake in
Trinidad, the central portion is a tarry petroleum, near the sides a
plastic asphalt, and finally that which is of almost rock-like solidity.
Hence we see that the solid residues from petroleum are unstable
compounds like the coals and lignites, and in virtue of their organic
nature are constantly undergoing a series of changes of which the final
term is combustion or oxidation. From these facts we might fairly infer
that asphalts formed in geological ages anterior to the present would
exhibit characters resulting from still further distillation; that they
would be harder and drier, i.e., containing less volatile ingredients
and more fixed carbon. Such is, in fact, the case; and these older
asphalts are represented by _Grahamite, Albertite_, etc., which I have
designated as asphaltic coals. These are found in fissures and cavities