448 Geological Society. 



interest in our local Geology, but placing in a just light the difficult 

 and obscui-e relations of that extensive series of beds which it de- 

 scribes. Nothing is now wanting, but the acquisition of good 

 maps by the extension of the Ordnance Survey, to complete our 

 geological acquaintance with the large portion of England de- 

 scribed in this Memoir. 



In Mr. Sedgwick's paper, the new red sandstone is considered as 

 constituting one great complex formation, between the lias and the 

 coal-measures, with two calcareous formations subordinate to it ; 

 one (the muschel-kalkstein,) in the upper part, which has not yet 

 been discovered in our country ; the other (the magnesian lime- 

 stone,) in the lower part, which the author has made especially the 

 object of his researches. 



But although the Muschel-kalkstein has not yet been observed, 

 and probably may not exist in any considerable force in Eng- 

 land, it would be premature to assert that its equivalent may 

 not still be detected among our strata; and this, with other cir- 

 cumstances, renders a good monograph of the new red sandstone 

 formation, in the central and southern counties, a desideratum of 

 importance. The general boundaries of the formation have been 

 correctly traced ; but the internal details remain to be investi- 

 gated : and, besides the necessity of searching in the upper part of 

 the formation for the equivalent of those beds which are so con- 

 spicuous on the continent, the relations of the porphyritic masses 

 of Devonshire and other places (which, it is remarkable, are found 

 in combination with the saliferous red sandstone, not only in various 

 parts of Europe, but even in India*) are still very obscure. The 

 publications of M. Charbautf, M. Elie de Beaumont :}:, and Messrs. 

 Oeynhausen, Dechen, and De la Roche § will be found to assist 

 materially in these investigations. 



The Magnesian limestone itself, according to Mr. Sedgwick, 

 admits of natural subdivision into five groups, which, in a descend- 

 ing order are: — 1. A series of red sandstone and marl, superior to the 

 dolomites, and subdivided into two portions, the equivalents of the 

 keuper and the hmter-sandstein. — 2. Limestones, containing magne- 

 sia and beds of dolomite, unequally diffused, but in much less pro- 

 portion than in the lower parts of the series. — 3. Red marl and gyp- 

 sum, comparatively of small extent. — 4. The great central deposit 

 of yellow limestone, exhibiting various modifications of dolomite, 

 frequently concretional, in some cases oolitic ; all of which appa- 

 rently result from internal change of structure, subsequent to the 

 mechanical deposition of the mass. These last formations (4, 3, and 

 2,) represent the Rauchwacke, Asche, and foliated Stinkstein, the brec- 

 cias, and gypsum of the Thuringerwald. — 5. Variegated marls, with 



* Geological Transactions, Second Series, vol. i. page 160. 



-f- " Environs de Lons le Saunier." — Annales des Mines, 1819, V. 579. 



j " Observations sur quelques Terrains secondaires du Systeme des 

 Vosges :" Paris, 1828: also published in the Annales des Mines for 1827- 



§ " Geognostische Umrisse den Rheinliinder, zwischen Basil and 

 Maintz:"2vols. 1825. 



irregular 



