Do these fuels result always and necessarily in one way from the decomposition of a pre-existing organic substance? Is it thus with the hydrocarbons so frequently observed in volcanic eruptions and emanations, and to which M. Ch. Sainte-Claire Deville has called attention in recent years? Finally, must one assign a parralel origin to carbonaceous matter and to hydrocarbons contained in certain meteorites, and which appear to have an origin foreign to our planet? These are questions on which the opinion of many distinguished geologists does not as yet appear to be fixed.