Relations of the Secondary Strata in the Isle of Arran. 23 



resembling- no other secondary limestone of the British series; and because 

 the same beds are surmounted by a carboniferous deposit containing three or 

 four of the most characteristic fossils of the true coal-measures. The mine- 

 ralogical character, and the greater part of the fossils of the upper red beds of 

 limestone, bring them also under the carboniferous order ; and if so, only prove 

 what is known to be true in many other places, that the mountain limestone 

 and coal-measures alternate with each other. It must, however, be allowed 

 that some of the fossils in this set of beds are also found in the magnesian 

 limestone overlying the coal-measures of Durham ; they may therefore by 

 some geologists be classed with that formation, in perfect conformity with the 

 order which we have attempted to establish. 



Lastly, the upper red sandstone and conglomerate have the character and 

 relations of the new red sandstone, and are therefore classed with that for- 

 mation. We may add, by way of confirmation to this mass of evidence, that 

 the preceding conclusions are rendered probable by the structure of the 

 nearest main-land of Scotland. 



If, however, we assume all this to be true, it must be allowed that there are 

 some points in which these formations differ from their equivalents in many 

 other parts of Great Britain : for the sandstones of the intermediate formation 

 are generally of a more brilliant white colour and less coherent texture than 

 the common gritstones of the coal strata; and the three formations are not 

 only perfectly conformable, but, as above stated, graduate insensibly into each 

 other. If, therefore, the rocks of the Arran section were assumed as the ge- 

 neral type of all contemporaneous deposits, there would then be no serious 

 objection to a classification attempted by some continental and British geolo- 

 gists; wherein all the rocks of the orders above described are considered as 

 belonging to one great formation of red sandstone, of which the carboniferous 

 series only forms a subordinate part : for as we extend our generalizations 

 we must necessarily diminish the number of our geological groups. AVe there- 

 fore think that this classification may have its advantages in comparing the 

 contemporaneous deposits of remote regions. It is certainly inapplicable to 

 the English secondary rocks, because the newer red sandstone is there always 

 unconformable to the carboniferous, and consequently finds its true place in 

 the superior order. This demonstrates that the carboniferous order of En- 

 gland was dislocated before the existence of the next superior order : but all 

 dislocations are probably, in a certain sense, local phasnomena; and on that 

 account we do not think that a want of conformity is one of the elements which 

 will much assist us in grouping together or in separating contemporaneous 

 deposits in distant parts of the earth. 



VOL. III. SECOND SERIES. P 



