Page:A Treatise on Geology, volume 1.djvu/105

 CH. V. with a second scale of organisation nearly as complete, and as distinctly related to time, higher in the ranks of creation, and therefore more sensibly dependent on physical conditions than the well known and justly valued series of remains of mollusca.

The orders of fishes, according to their scaly coverings, are four; viz.

M. Agassiz appears to have ascertained that the strata below the cretaceous rocks contain very few, if any, other fishes than such as are included in these orders.

To the last two orders with unenamelled scales belongs by far the greater proportion of existing species