316 Mr. MuRCHisoN on the Coal-field of Brora in Suthcr lands hire, 



any good natural sections. The progress of investigation has enabled us to 

 go still further. Certain genera and species of fossil shells have been shoven 

 to be so characteristic of deposits of a particular geological sera, that we have 

 in many instances been enabled to fix the epoch of a formation by zoological 

 characters alone ; where (in consequence of some local causes) all other evi- 

 dence has been wanting. The history of the Brora coal-field is a new instance 

 of this kind of generalization. The several parts of this deposit have been 

 brought into comparison with certain portions of the English oolitic series^ 

 solely by the help of zoological characters. This generalization is fully con- 

 firmed by the phasnomena presented on the Yorkshire coast. We have there 

 a repetition of the peculiarities of the Brora coal-field and some of the same 

 fossil plants; but still under circumstances which seem to put the great rela- 

 tions of the deposit entirely out of doubt. 



2. If the preceding remarks show the great importance of attending to the 

 fossil history of our several formations^ the facts stated in the former part of 

 this paper at the same time prove the absolute necessity of examining the 

 mineralogical structure and relative position of the subordinate beds^ where- 

 ever they are exhibited in natural sections. It is only by a comparison of all 

 such characters, that geological induction can be established on a firm basis. 

 Several of the organic remains in the annexed catalogue are entirely new. It 

 is, therefore, probable, that, in remote parts of the European basin, there 

 may be formations of lignite of the same age with the Brora coal, in which 

 the suite of fossil remains will be found to present very few analogies with 

 those which distinguish the oolite of England. Every thing with which we 

 are acquainted tends to show, that Nature in modifying the solid parts of the 

 earth's surface has acted by very general laws. There appear to be no 

 sudden transitions in the zoological history of the same formations during 

 their range through different latitudes. Every new fact in their natural his- 

 tory becomes therefore of importance; inasmuch as it may give us a new 

 term of comparison between our own strata and those in distant countries. 

 And we may venture to hope, that, as minute details become multiplied, many 

 more new terms of comparison will be discovered, which may form so many 

 connecting links between distant contemporaneous deposits ; so that we may 

 not only generalize with more certainty in neighbouring regions, but be 

 enabled to extend our inferences to the remotest parts of the Earth. 



3. If we assume that the coal-fields at Brora and on the Yorkshire coast 

 are contemporaneous, and also the equivalents of tiie several formations which 

 intei-vene between the Oxford clay and the lias ; we must at the same time 

 admit, that the causes which produced the oolitic deposits in the central and 



