What is meant by ‶succession″ by palaeontologists is the fact that the earth has, during successive geological epochs, been peopled by successive races of animals and plants. The general admission of this fact may somewhat obscure its importance, but in reality it forms the keystone of palaeontology as applied to geology. Whilst all admit the general fact of ‶succession,″ there are two leading and opposing views as to the manner in which succession has been effected. On one view, the succession and progression of organic types in past time, with which the geologist is familiar, is believed to be due to the creation of successive faunae and florae, each of which appeared in its entirety at the commencement of a geological period, lasted through the period (as a whole), and then finally disappeared at the close of the period, to make room for another and higher fauna and flora. This view need not be discussed here; for it may at once be said that it cannot be retained, in an unmodified form, in the face of ascertained and admitted facts. Upon this view it is inconceivable that certain forms should have escaped the general destruction of life which is assumed to have taken place at the close of each great period, and should have been thus transmitted to the following period. And yet the occurrence of ‶persistent″ types of life is undeniable, and, indeed, far from uncommon. If, for example, we suppose that all the animals which lived in the