Prior to the time The Origin of Species was written, the geologic time scale in its modern form was already fully developed. Scientists of Darwin's day did not equate geologic succession with evolution, nor should we today. One reason is that geological succession does not reveal how new species came into existence, it only reveals when. Another reason is that the order of appearance found in the fossil record is, as a general rule, systematically backwards from the major predictions of Darwinian theory. Geological succession is often looked upon as primary evidence for the fact of evolution.
Amoebas appear before fish, and fish before philosophers.
In the popular view, this succession from simple to complex is evidence for evolution. Geological succession, however, does not necessarily proceed from simple to complex. For example, trilobites, among the most advanced of the arthropods, are the first arthropods to appear in the geological record. The early metazoans were anything but simple. The complexity of the early metazoans, however, is but a wrinkle in the irony of Darwinism.