There appear to be two or three obstacles in the way of a proper classification of fossil fishes, and of obtaining sufficient data to establish the earliest period cf the earth's formation, during the deposition of which any particular fish existed, the principal obstruction being caused by the disconnected manner in which the researches have been carried on; for palæontologists; as a rule, confine themselves to the fauna or flora of the formations that are most exposed in their localities, either by nature or by the hand of man.