2 



BRITISH FOSSIL CORALS. 



It is this coming in of the same species at various positions in a large formation and 

 their association with difiFerent groups of species that renders Palseoutology of more or less 

 uncertain value in the exact determination of the age of strata. 



But it is this varying vertical range of species in different areas and their association 

 with different groups of forms that points to an ever-changing life-scene, to migration of 

 faunae, to changes of physical conditions, to variation in the intensity of competition, to 

 the rise of dominant and the decay of feeble forms, and to all those external agencies which 

 affect the inherent power of variation peculiar to the animated nature of this world, where 

 no two things are exactly alike. 



The persistence of a species in a succession of strata, and its consecutive association 

 with different groups of competitors and contemporaries, is constantly observed in the Lias, 

 taken as a whole ; and it is the strongest fact that can be adduced against the almost 

 exploded notion of a series of cataclysmal destructions and of successive creations of 

 beings occurring at intervals which are denoted by changes in physical geology. It is 

 necessary to assert that those doctrines are not quite exploded, for they have a deep hold 

 on the minds of many who have only a limited area of geological observation. The 

 disposition to limit the possibility of the occurrence of certain specific forms to definite 

 vertical ranges arises from a partial belief in those ideas, and they are apparently 

 strengthened in the force of their application when physical breaks accompany palseonto- 

 logical changes. 



Here the question concerning the physical causes which permit of and assist in the 

 preservation of dead organisms must be considered in reference to those which have a 

 diametrically opposite effect. 



If it be admitted that when the terrestrial conditions are in statu quo the preservation 

 of organic remains from destruction is hardly possible ; that during elevation of areas the 

 entombment and fossilization of organisms is equally unlikely, and that a gradual 

 depression of the surface is in the majority of instances necessary for the preservation of 

 deposits, it becomes evident that, whilst the physical break has a diminished value in its 

 relation to the persistence of the life of species, the existence of a species in a considerable 

 series of strata which could not have all been deposited during a continuous and uninter- 

 rupted sinking of their area becomes most suggestive. Taken in combination with the 

 remarks which have preceded, it is suggestive of the evident want of relation between 

 the formation of strata and the origin and decadence of the species of the period ; and it 

 points out that no Strati graphical Palacontogeology can be perfect in a classificatory 

 sense, and that zones of species may have little to do with the notion of time. 



With an ever-progressing animated nature there are and have ever been associated 

 terrestrial and inorganic changes. There is no definite connection between them, and 

 hence our classificatory systems have an increment of error which is constantly rising to 

 the surface when the pure physical geologist and the pure palaeontologist argue upon their 

 own bases concerning the age of strata. 



