Geological Society. 449 



irregular beds of compact limestone, Zechstein. Tliis formation is not 

 co-extensive with the yellow limestone, but its place is constant; and 

 its subordinate marl-slate is particularly distinguished by its Fossils; 

 among which ai'e impressions of ferns, and the remains of fishes, 

 some of them identical with those of the copper-slate of Thuringia. 

 — 6. And lastly, an extensive deposit of coarse siliceous sandstone 

 (^rothe-todte-liegende,) of very unequal thickness; the upper beds 

 of which are sometimes unconformable to the limestones which rest 

 upon them. 



It is satisfactory therefore to find, that the great mass of strata, 

 from the oolites down to the coal, admits precisely of the same 

 subdivisions in the north of England, as upon the continent. And 

 with respect to the theory of these magnesian formations, Mr. 

 Sedgwick ascribes their production to the mechanical destruction 

 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 scries 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 tracl;s above 

 mentioned, is accidental, and comparatively of small extent. 



The researches of Professor Sedgwick and Mr. Murciiison 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 ma.ssus beneath ; and confirm the gene- 

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



• Ann. des Mines, 1^*27, •• -l-^l- 

 N. S. Vol. ,-,. No. .'JO. .fiiiir 1829. 3 M detached 



