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dead exuvise; and in this difference is found an ample explanation of the absencefrom fossil fauna; and florae of a multitude of genera, which, from the perishablecharacter of their substance, cannot be expected to leave any permanent relics behindthem. The natural habitat of most fossil species indicates the necessity of cautionin reasoning on an imperfect fauna, which in our opinion ought not to be ascribedto the absence of certain classes of animals in the fossil epochs, but rather to theimprobability of finding their relics in deposits such as those we examine.
A very limited local deposit of the Oolitic period, the Stonesfield slate, gave to lightthree species of the Marsupial order, an order now of very limited distribution, andthereby brought into strange connection the fauna of that remote epoch with theexisting fauna of Australia . If the minute patch which produced so great a scientifictreasure be compared with the whole extent of the Oolitic formations already knownand studied, how small will appear the chance that such a discovery should ever havebeen made; and yet this fact is sufficient to demonstrate the truth, that warm-blooded Mammals of the Marsupial order did exist at the Oolitic period; and as thegenera belong to the insectivorous type of the order, the fact proved in anticipationthat insects must also have existed: and that such was the case has been shewn bythe discovery of their relics in the Oolitic strata. Nor is this all; for with ProfessorOwen we must also assume, that the existence of small quick-breeding Marsupials ofan insectivorous type justifies us in believing that the other types of that great orderexisted also, and that the harmonies of animal life were maintained then as now.Can it, for instance, be doubted that the large carnivorous Marsupials were then inexistence, to prey upon the small and quickly multiplying insectivorous species?And such are the remarkable truths brought home to our convictions by the acci-dental and almost improbable discovery of a few fossil fragments, and which wouldhave remained unknown had not that discovery been made.
It will be observed that the author of the ‘ Index Pateontologicus' carries backthe existence of Mammals to the Keuper or newer member of the Trias; and shouldsuch determination be fully established, the difficulty of admitting that no Mammalsexisted in the Cretaceous 1 epoch is increased, and the inquirer is forced to concludethat the same fortunate chance which gave, as it were, a glimpse at this highermember of the fauna of the Oolites is only wanting to display to us animals of equallyhigh organization in the Chalk. It is, indeed, in the Cretaceous system that the firstclear indication of another great class of the animal kingdom is obtained, namely, ofBirds; and to this casual and local evidence of a fact so striking the same remarksshould be applied, so as to extend its bearing from the simple occurrence of a fewrelics of two species of birds to the probable existence of other animals in habits andother relations connected with them. It is thus that the fauna of each of these re-mote epochs may be built up,—speculatively, it is true, but yet reasonably,—fromthese isolated individuals, just as in the hands of the great Cuvier the whole body ofan extinct animal was first restored from the examination of a few of its fragments.Or if we reverse the course of our reasoning, and suppose that the whole of ournow existing animals and plants were suddenly annihilated, and, after the lapse oftwo or three thousand years, Man, having again appeared on the earth, were toendeavour to build up a natural history system of the past epoch from the relics hemight discover in distantly scattered portions of the mud and sand-banks of formerbays and estuaries, placed within the scope of his observation by the great catastrophewhich had accompanied the destruction of organic life,—can we doubt that his taskwould be most imperfectly performed, and that th would be a large proportion todiscover of the animals then extinct ? Considering, therefore, that the rare occur-rence of the fossil relics of Mammals, Birds, Myriapod *, Spiders, and Insects, should