{ | Old Red Sandstone.| Scorpions, Fish, Batrachians, | { | | etc. | { +-------------------+--------------------------------+ Primary. { | Silurian. | | { +-------------------+--------------------------------+ { | Cambrian. | Shell Fish, Sponges, Molluscs, | { | | Crustaceans, Worms, etc. | { +-------------------+--------------------------------+ { | Huronian. | } | { +-------------------+--}-----------------------------| { | Laurentian. | } Protozoa. | +===================+================================+ | AZOIC. | | In the Cambrian age, we obtain a vast and varied accession of living things, which appear at once, as if by a sudden and simultaneous production of many kinds of animals. Here we find evidence that the sea swarmed with creatures near akin to those which still inhabit it, and nearly as varied.... Had we been able to drop our dredge into the Cambrian or Silurian ocean, we should have brought up representatives of all the leading types of invertebrate life that exist in the modern seas--different, it is true, in details of structure from those now existing, but constructed on the same principles, and filling the same places in nature. In the latter half of the Palæozoic we find a number of higher forms breaking upon us with the same apparent suddenness as in the case of the early Cambrian animals. Fishes appear, and soon abound in a great variety of species, representing types of no mean rank, but, singularly enough, belonging in many cases to groups now very rare; while the commoner tribes of modern fish do not appear. On the land, Batrachian Reptiles now abound, some of them very high in the sub-class to which they belong. Scorpions, spiders, insects, and millipedes appear as well as land-snails: and this not in one locality only, but over the whole northern hemisphere.... Nor do they show any signs of an unformed or imperfect state.... The compound eyes and filmy wings of insects, the teeth, bones, and scales of batrachians and fishes; all are as perfectly finished, and many quite as complex and elegant, as the animals of the present day.