4 Mr. Charlesworth oji the Crag, and on ascertaining 



distinct science. Such are the changes of climate anterior to the 

 historic aera, the comparative duration of species, and the wide 

 geographical range which some extinct organisms enjoyed, 

 having apparently existed at the same period over an immense 

 extent of surface. These and numerous other inferences of 

 a similar kind often depend in a great measure upon the ac- 

 curacy with which we can refer individual beds or groups of 

 strata' to particular deposits, and trace these separate forma- 

 tions in widely remote localities, from observing the occurrence 

 of certain corresponding phaenomena. Philosophically speak- 

 ing, it is, perhaps, of most importance in the fossil iferous 

 rocks to make out the natural subdivisions (if such really 

 exist) of the two extremes of the series; and in arriving at any 

 generalizations analogically deduced from our present insight 

 into the laws of nature, those deposits offer the most legiti- 

 mate grounds for rational speculation which appear to have 

 originated during an aera that impinges upon the present. 



The most novel feature in the organic remains of the crag, 

 considering the whole deposit as referrible to one period, is the 

 occurrence of so many recent mammiferous species in one 

 bed, and so large a series of extinct corals in the other. Now 

 if the coralline crag be older than the stratum in which these 

 mammalian remains are found, we have no longer this asso- 

 ciation of extinct forms in one class of the animal kingdom 

 with recent types belonging to a very different order. A geo- 

 logist desirous of instituting a comparison between these ter- 

 tiary deposits and those in other parts of Europe, might meet 

 with the equivalent of one only, assuming the red and coralline 

 crag to be distinct. It would then become a question of great 

 importance whether the organic remains included in the two 

 series ought to be considered collectively or not, in endeavour- 

 ing to establish an agreement with the fossils of supposed 

 corresponding strata in distant localities. 



Passing to generalizations of a different character, I will 

 select one which I think illustrates in a particularly forcible 

 manner the importance of allowing full play to the present 

 investigation. The occurrence of some extinct mammiferous 

 quadrupeds in deposits containing exclusively or nearly so 

 recent Mollusca^ has led Mr.Lyell to attribute a longer dura- 

 tion of species to the latter. Applying this argument to the 

 fossils of the crag, we find conditions of another kind ; for the 

 forms which are most widely removed from existing types 

 occur among the corals, while the majority of the mammiferous 

 animals eitlier closely resemble such as are now living, or 

 can be identified with those which are imbedded in the al- 

 luvial or lacustrine depdsits above the crag. Hence we might 

 infer the short duration of the spe^gi|Bfe}' corals when com- 

 ,.... I . :.u .!... ^'Jammalia, and con^tTS^tlv the still shorter 



