Palæontology is defined as ‘the science which treats of fossil remains both animal and vegetable.’ This principle of the continuity of life from age to age may be considered as one of its definite acquisitions. There is no single point of geological time at which it can be said, ‘at this epoch clearly all old species had passed away, all kinds of life had become new.’ Not only is there no indication of such a break, but there is the strongest evidence against any such having ever occurred. In spite, however, of the completeness of the evidence required for proving this single conclusion, the general incompleteness and enormous deficiencies in some parts of the palæontological record can be established beyond dispute. We are in the position of a man who has kept the title-deeds to a large estate, while almost all the estate itself has been buried under the encroachments of the sea. Here and there some old landmarks may be discernible far out in the waters, showing the extent of what had once been meadow and woodland, farm and garden, but unable to show how these were distributed, or to exhibit any of their details. Mr. Parfitt, in his paper on ‘Fossil Sponge Spicules,’ told the Devonshire Association last year (1870) that we have evidence more or less exact of sponges in a fossil state as far back in time as the Silurian system, mentioning specimens of _Acanthospongia Siluriensis_, _Cliona antiqua_, and _Cliona prisca_, and stating in regard to the two latter that the genus is still in our own seas. He then referred to large masses of a fossil in the Devonian rocks of Cornwall, believed by some to be sponges, and by others to be the remains of fish. That these are in reality fish-remains has, in fact, been shown pretty conclusively[59]. From this point, however, up to the Great Oolite, Mr. Parfitt tells us that scarcely a vestige of the sponges is to be found, although since that time they have been very abundant. Between the Silurian and the Great Oolite the interval of time must have been enormous. It is occupied by a vast series of sedimentary rocks, embracing very varied mineral characteristics. From this series our museums have been, and are still being, supplied with vast heaps of fossil organic structures, including among numerous others, plants and corals and fish and reptiles. Through all that protracted period there is no reason to suppose, in regard to the outer rind of the globe, that the general conditions of earth, air, and water were other than they are now. All England may have been under water; delicate creatures may have wintered at the North Pole for the sake of its genial climate; and an infinity of other local and temporary differences may have prevailed, without making the habitable globe of those days essentially different from our own. The laws of chemistry and mechanics, the laws of heat and motion, must have been just the same as they are now. Then, as now, there must have been oceans and continents, winds and