100 Rev. A. Sedgwick on the Geological Relations and 



off*. Again, the great internal movements vvliich took place while many of 

 the strata were passing into a solid state, must have been unfavourable to the 

 process of petrifaction, and may have destroyed the imbedded shells and 

 corals. Under such circumstances they could not form casts : they would, 

 therefore, probably disappear altogether ; for they very rarely, under the 

 most favourable circumstances, are seen in the form of perfect petrifactions 

 exhibiting the shelly covering. In this manner we may perhaps account for 

 the non-appearance of organic remains in many extensive parts of the de- 

 posit, compatibly with the hypothesis which has been just stated. 



If the marl-slate and compact limestone of a preceding section (§ 2.) has 

 been properly identified with the kupfcr schiefer and zechstein, it follows that 

 the great deposit of yellow limestone last described must be the equivalent of 

 a part of the upper system of calcareous strata in the Thuringerwald. The 

 descriptions of this upper system, given at length by Freiesleben and abridged 

 by D'Aubuissonf, fully bear out the conclusion. We there meet with most 

 of the modifications which have been already enumerated ; the same cellular 

 strata (rauchicacke) ; the same foliated and fetid beds (stinkstein), associated 

 with, and passing into, masses which are pulverulent {asche) ; the same con- 

 temporaneous breccias ; the same small concretionary structure rarely passing 

 into oolitic; the same confusion of chemical and mechanical structure; the 

 same concretions of carbonate of lime ; and the same frequent passages of one 

 modification into another. So that three-fourths of the descriptions given in 

 the abridgement of D'Aubuisson might be applied, almost word for word, to 

 the corresponding parts of the English series. 



There are at the same time, as might be expected, some points of difference. 

 In England the concretionary structure seems to be more perfectly developed 

 than in Germany. On the contrary, the great masses of rock salt which in 

 Thuringia are subordinate to the calcareous beds, have no adequate repre- 

 sentatives in our magnesian limestone ;{:. The alternating gypseous beds of 

 Thuringia may perhaps be represented, though under a modified form, by 

 the deposit which I now proceed to describe. 



* In the same way the organic spoils have probably disappeared from many of the incoherent 

 portions of the formations (such as the Woburn sands) under the chalk. A curious instance of 

 the gradual absorption of certain organic remains in a recent deposit, is given by Mr. Lyell in a 

 preceding part of the Geol. Trans. (See Second Series, vol. ii. p. 87, &c. «&c.) 



t Tratte de Geognosie^ vol. ii- p. 344. 



X I had been informed by the Rev. J. Holme, that in analysing various dolomites from this 

 formation, he had found traces of muriate of lime ; but I was not aware that any trace of muriate 

 of soda had ever been discovered. He has, however, since examined some large specimens which 

 I procured from the red beds near Mansfield, and has obtained beautiful cubes of muriate of soda 

 from them. The Thuringerwald salt is therefore not altogether without its representative in the 

 English series. For an analysis of one of the red beds alluded to, see p. 84, note. 



