It appears still further, that all the great changes in the character of fossil Fishes take place simultaneously with the most important alterations in the other classes of fossil animals, and in fossil vegetables; and also in the mineral condition of the strata.[1]
It is satisfactory to find that these conclusions are in perfect accordance with those to which geologists had arrived from other data. The details that lead to them, will described by M. Agassiz, in a work of many volumes, and will form a continuation of the Ossemens Fossiles of Cuvier. From the parts of this work already published, and from communications by the author, I select a few examples illustrating the character of some of the most remarkable families of fossil Fishes.
It appears that the character of fossil Fishes does not change insensibly from one formation to another, as in the case of many Zoophytes and Testacea; nor do the same genera, or even the same families, pervade successive series of great formations; but their changes take place abruptly. at certain definite points in the vertical succession of the strata, like the sudden changes that occur in fossil Reptiles and Mammalia.[2] Not a single species of fossil Fishes has
- ↑ The genera of Fishes which prevail in strata of the Carboniferous order are found no more after the deposition of the Zechstein, or Magnesian limestone. Those of the Oolitic series were introduced after the Zechstein, and ceased suddenly at the commencement of the Cretaceous formations. The genera of the Cretaceous formations are the first that approximate to existing genera. Those of the lower Tertiary deposites of London, Paris, and Monte Bolca, are still more nearly allied to existing forms; and the fossil Fishes of Oeningen and Aix approximate again yet closer to living genera, although every one of their species appears to be extinct.
- ↑ M. Agassiz observes that fossil Fishes in the same formation present greater variation of species at distant localities, than we find in the species of shells and Zoophytes, in corresponding parts of the same formation; and that this circumstance is readily explained by the greater locomotive powers of this higher class of animals.
