119 



of rocks of the carboniferous order ; stating however two facts, as 

 yet imperfectly explained ; 1st. The greater abundance of magnesia 

 in the limestone formation than could have been derived from the 

 dolomites of the carboniferous order; — and, 2ndly, The larger pro- 

 portion of magnesia in some of the beds, than is found in the true 

 dolomites ; an excess which M. Elie de Beaumont has shown to 

 exist also in the corresponding strata of the Vosges. 



The want of conformity between the superior members of our 

 series and the coal-measures, forms, it is well known, a prominent 

 feature in the structure of the west of England : — which, besides 

 its great importance to the coal-miner, has been supposed to mark 

 an epoch in the order and circumstances of deposition; since a 

 similar want of conformity exists in the north-west of France and 

 Belgium, — and from recent observation has been found also on the 

 flanks of the Vosges mountains*; where the shafts for obtaining 

 coal are frequently cut through the superior beds, to reach the 

 unconformable strata beneath. It was a question therefore, of con- 

 siderable interest, to determine how far this want of conformity 

 might extend : and Messrs. Sedgwick and Murchison have shown 

 that in Scotland, especially on the shores of the Isle of Arran, 

 where a very distinct section is disclosed, the coal-measures are 

 conformable in position to the incumbent strata ; and that a gradual 

 transition may be observed, in ascending, from the old red-sandstone, 

 to the carboniferous series, with plants of the same species as of the 

 English coal-measures ; from which again there is a gradation into 

 a series of conformable strata, supposed to be identical with the 

 new red-sandstone of England. Hence it is not improbable that 

 more extended inquiry will prove the conformable arrangement to be 

 the more general one ; and that the want of it, within the tracts above 

 mentioned, is accidental, and comparatively of small extent : and 

 this may be accounted for, by supposing, either that some local 

 dislocation may have deranged a portion of the strata which would 

 otherwise have been conformably disposed ; — or, that an interval 

 occurred between the deposition of the now discordant members, 

 of such duration, and attended with such agencies, as to admit of 

 considerable change of surface in the mass of strata first deposited. 



The researches of Professor Sedgwick and Mr. Murchison in 

 Scotland, contained in papers one of which has been already pub- 

 lished, throw much light upon the relations of the lower part of 

 our series to the crystalline masses beneath ; and confirm the gene- 

 ral diffusion in that country of our secondary strata ; — though in 

 detached portions, and generally accompanied by indications of 

 disturbance, obviously proceeding from the primary masses on 

 which they at present repose. It would exceed the limits to which 

 I am here confined, to detail the results of which these memoirs 

 give an account : the general inferences are, — 1. The identity with 

 the secondary rocks of England, of the strata in the Western-Islands, 



* Ann. des Mines, 1827, i. 431. 



