It is apparent that nothing more than the value of a hypothesis can be attached to these speculations. Nothing indicating sublimation has been observed where the theory supposes it to have taken place; the operation of a natural chemical distillation is not proved by any evidence of such a process having anywhere taken place. The opinions of MM. Daubrée, Lartet, and Coquand, in favor of a chemical origin, being based upon studies of the formations themselves, are regarded as being of more substantial value. These authors, however, are judged to have erred in confounding the original formation of the substances with their appearance where they are found—which, in the view of the author, are two very different affairs.
A bituminous limestone of the Val de Travers, Switzerland, is formed almost wholly of shells, echini, and similar fossils, held together by a calcareous cement. Some of these fossils are only casts, the shell having been absorbed, while the interior, otherwise empty, is partly filled with a viscous bitumen, the quantity of which is proportioned to the size of the shell. In the smaller brachiopods there is only enough to color the inclosing rock a chocolate brown; in the larger ones it forms a lump which is softened by warming. The bituminous limestone of Auvernier is marked by infinitely numerous little cavities, such as are seen in tufas, which are made visible by the presence of a brown substance, the residue of a volatilized bitumen. It also contains casts or impressions of fossilized shells, and in these again are deposits of brown or blackish substance—the organic matter of the mollusk, transformed into bitumen. The cavernous or breccialike rock of Bevais, a few miles south of Auvernier, contains what we might perhaps call glutinous inclusions—cavities corresponding with the internal part of the fossils, colored brown with organic matter. There are also real pockets of viscous bitumen, which liquefy under a slight increase of temperature. A closer examination of the cavity shows that it is the result of the destruction of an astræan polyp. Of the association of petroleum and fossils in the United States, an observation has been recorded by M. Daubrée of petroleum occupying the cavities of fossils—orthoceratites, brachiopods, and corals, as well as porous parts of the rock—in some of the beds of the Ohio Valley; and a statements by MM. Fuchs and Launay, that "a remarkable characteristic of the Canadian oil is the profusion of remains of mollusks and crustaceans, with some traces of marine vegetation, which it contains. This is one of the most serious facts on which an organic origin is attributed to petroleum."
Of the occurrence of these hydrocarbons, including also natural gas, a review of all the theories and evidences leads us to the conclusion that stratified deposits of asphalt, bitumen, and petro-
