There has been no lack, in the history of geological science, of suggestions as to how our knowledge may be advanced upon those obscure questions which yet ask for solution, both in the physical and palæontological departments of the study. Sometimes, by a surprising intellectual endeavour, we have been carried up to the moon, and asked to discover where its missing waters are, without which our useful satellite appears to be a sort of ‘house to let,’—the idea having got into the mind which originated the enquiry, that the earth had appropriated the said waters for the necessities of a supposed cataclysmal epoch. Also, we have been taken down, by speculative thinkers, at divers times, to depths beneath our terraqueous surface, and asked to pin some fundamental articles of faith upon schemes which show all existing there to be either fire, or water, or a zone of meterorite-mineral, or one of soild steel, or that, nothing existing there, the interior of our planet is a vacuum.