hunter's posthumous paper on fossils. 305 



their science as that which treats of the structure and changes of the 

 ' crust ' or ' surface ' of the earth. 



Thus the proper aim of geological investigation, the right way of 

 investigating, and the true extent of the field of investigation, are, at 

 the outset, recognized and defined by Hunter. 



" Finding," he remarks, " upon land more parts of marine than ter- 

 restrial animals preserved, and at considerable depth, it naturally leads 

 to the idea of sea-animals at least having undergone this process at the 

 bottom of the sea ; and if so, then as that [stratum] in which they are 

 found is now land, and as we find parts of land- animals and vegetables 

 preserved nearly in the same manner, it leads us into a more extensive 

 investigation of the permanency of the situation of the waters ; and in 

 this inquiry we shall find that wherever an extraneous fossil is enclosed 

 or imbedded, the surrounding native matrix was accumulated, disposed, 

 or formed into that mass at the same time." — P. iv. 



Here Hunter enunciates another important principle, the coevality 

 of the fossils with the mineral strata in which they are found. This 

 principle has since been abundantly established ; the use of fossil 

 organic remains, illustrated by Hunter's figure of human monuments 

 and memorials, depends upon the demonstration of this proposition as a 

 general rule. I do not find it so definitely laid down in geological 

 writers prior to Hunter ; although it was evidently appreciated in a 

 certain degree, and with reference to particular strata, by some of 

 Hunter's predecessors. 



The exceptions to the rule arise from the formation of one stratum 

 out of the ruins of a preceding fossiliferous stratum, when the fossils of 

 that older stratum become, together with their matrix, a part of the 

 newer one, with which, however, those fossils are far from being 

 coeval in respect of the period when they actually became fossil. 

 Petrified bones of Plesiosaurus, e. g., have been transmitted to me, 

 together with unpetrified bones of the beaver, from the comparatively 

 recent ' till ' of Cambridgeshire, the plesiosaurian remains having been 

 washed out of the subjacent gault, when the sea finally retired from 

 the uprising land. Such ' derivative' fossils were nevertheless actually 

 inclosed or imbedded in the newer tertiary matrix when it " was 

 disposed or formed into the mass," now called ' till.' The exceptions of 

 such derivative fossils are, however, comparatively rare, and do not 

 affect the conclusions, as to the relative age of a stratum, afforded by 

 its obviously and much more abundant proper organic remains. 



" It might be supposed that the fossils of sea-animals would be found 

 in eveiy known substance ; because it is natural to suppose, as most 

 substances have been formed at the bottom of the sea, that every kind 



x 



