The productions of the land seem to have changed at a quicker rate than those of the sea, of which a striking instance has been observed in Switzerland.

There is some reason to believe that organisms high in the scale, change more quickly than those that are low: though there are exceptions to this rule.

The amount of organic change, as Pictet has remarked, is not the same in each successive so-called formation.

Yet if we compare any but the most closely related formations, all the species will be found to have undergone some change.