For anything that geology or palaeontology are able to show to the contrary, a Devonian fauna and flora in the British Islands may have been contemporaneous with Silurian life in North America, and with a Carboniferous fauna and flora in Africa.  Geographical provinces and zones may have been as distinctly marked in the Palaeozoic epoch as at present, and those seemingly sudden appearances of new genera and species, which we ascribe to new creation, may be simple results of migration.

It may be so; it may be otherwise.  In the present condition of our knowledge and of our methods, one verdict—­“not proven, and not proveable”—­must be recorded against all the grand hypotheses of the palaeontologist respecting the general succession of life on the globe.  The order and nature of terrestrial life, as a whole, are open questions.  Geology at present provides us with most valuable topographical records, but she has not the means of working them up into a universal history.  Is such a universal history, then, to be regarded as unattainable?  Are all the grandest and most interesting problems which offer themselves to the geological student essentially insoluble?  Is he in the position of a scientific Tantalus—­doomed always to thirst for a knowledge which he cannot obtain?  The reverse is to be hoped; nay, it may not be impossible to indicate the source whence help will come.

In commencing these remarks, mention was made of the great obligations under which the naturalist lies to the geologist and palaeontologist.  Assuredly the time will come when these obligations will be repaid tenfold, and when the maze of the world’s past history, through which the pure geologist and the pure palaeontologist find no guidance, will be securely threaded by the clue furnished by the naturalist.

All who are competent to express an opinion on the subject are, at present, agreed that the manifold varieties of animal and vegetable form have not either come into existence by chance, nor result from capricious exertions of creative power; but that they have taken place in a definite order, the statement of which order is what men of science term a natural law.  Whether such a law is to be regarded as an expression of the mode of operation of natural forces, or whether it is simply a statement of the manner in which a supernatural power has thought fit to act, is a secondary question, so long as the existence of the law and the possibility of its discovery by the human intellect are granted.  But he must be a half-hearted philosopher who, believing in that possibility, and having watched the gigantic strides of the biological sciences during the last twenty years, doubts that science will sooner or later make this further step, so as to become possessed of the law of evolution of organic forms—­of the unvarying order of that great chain of causes and effects of which all organic forms, ancient and modern, are the links.  And then, if ever, we shall be able to begin to discuss, with profit, the questions respecting the commencement of life, and the nature of the successive populations of the globe, which so many seem to think are already answered.