PURBECK FORMATIONS. Ill 



not with ITypsiprymnus amongst the harmless saltatorial Herbivora, it will onlj' be further 

 j^roof of the worth and truth of the principle which Cuvier laid down as our guide in 

 such dark routes in Palaeontology. 



§ XX. CONCLUSION. 



The number of Mammalian species discovered in deposits of Mesozoic antiquity 

 supports the inference of progressive advance. These early, if not initial, forms of the 

 class are referable, on more or less demonstrative evidence, to the lyencephalous sub- 

 class ; to that in which the brain has received least addition to its avian and reptihan 

 status. Where the marsupial character is least clear in these little fragmentary fossils, 

 the alternative from the plainer evidence is to the lissencephalous subclass. And it may 

 well be, since, amongst the Lissencephala, the modern Insectivores show the first steps in 

 the development or extension of the hippocampal commissure, entitling it to be called 

 ' corpus callosum,' or ' supra-ventricular cross-band,' tliat intermediate steps in this 

 cerebral progress may have been made by some of these Mesozoic Mammals, in 

 which the marsupial characteristics are least differentiated from the modern Insectivorous 

 types. 



To the objection of the 'Uniformitarian,' that the fossil record of Mesozoic Mammalogy is 

 too imperfect for inference, we may ask, — when he would be pleased to admit the evidence 

 to be sufficient to affect belief or judgment ? Is any class of fossils from any geological 

 formation so extensively known as to justify the assumption that nothing exceptional or 

 contradictory to conclusions therefrom may not ultimately turn up? Can the Zoologist 

 demonstrate that he knows all the existing species of any one genus, order, or class ? 

 Does any misgiving of the imperfection of the records of living species warrant the sup- 

 pression of the instinctive tendency to generalise from the facts at hand ? Or, on the 

 other hand, give liberty to guess or theorise without or against such facts? 



In the present Monograph I submit evidence from three distinct and probably, as to 

 time, very remote stages of that grand geological group of deposits, called 'Mesozoic' There 

 is a highly suggestive concurrence in the evidence, as at present derived, from Rhsetic, 

 Lower Oolitic and Upper Oolitic periods. To my mind it has a significance ; and I believe 

 its meaning and teaching to be against the uniformitarian assumption, and in favour of 

 " orderly succession and progression due to Natural Law or Secondary Cause." ^ 



Mesozoic Mammalian life is, without exception, on this evidence, low, insignificant in 

 size and power, adapted for insect-food, for preying upon small lizards, or on the smaller 

 and weaker members of their own low mammalian grade. 



1 Owen, ' On the Nature of Limbs,' 8vo, 1849, p. 86. 



