122 Rev. A. Sedgwick on the Geological Relations and 



between the coal-measures and the superior deposits ; in some parts of York- 

 shire there is no such want of continuity, and the h>wer red sandstone seems 

 to form a connecting- link between the carboniferous order and the group of 

 the new red sandstone. Moreover, the fossils of the magnesian limestone have 

 little resemblance to the fossils of the lias and the oolites, but liave several 

 o-enera and species in common with those of the mountain limestone. 



4. The new red sandstone series in the south-western coal districts admits 

 of three natural divisions ; viz. dolomitic conglomerate, red sandstone, and 

 red or variegated gypseous marls^ which are immediately surmounted by the 

 lias*. It therefore follows, that of the seven subdivisions above established, 

 the five lowest are, in the south-western parts of England, represented by the 

 dolomitic conglomerate. Hence these dolomitic conglomerates, and the con- 

 temporaneous conglomerates in the valleys of Somersetshire and Devonshire, 

 are not merely the equivalents of the rothe-todte-Uegende, as has been some- 

 times assumed, but are in the place of a great part of the Thuringerwald 

 system. 



5. The preceding conclusion seems to be perfectly secure ; but we may, if 

 1 mistake not, advance a step further. The lower red sandstone (or rothe- 

 lodte-liegende) is best developed in those extensive tracts of Yorkshire where 

 the overlying deposits are very nearly^ if not exactly, conformable to the coal 

 formation, and appears to thin oft' in those places where the coal-measures are 

 most dislocated : moreover, it is under such circumstances that it exhibits in 

 mineral structure a gradation between carboniferous gritstone and new red 

 sandstone. Now, there is an absolute disruption between every part of the 

 dolomitic conglomerates and the coal-measures in the west of England; nor 

 do these conglomerates contain any extensive beds which bear the least re- 

 semblance to the lower red sandstone : but they arc nearly identical with 

 some masses which in the north of England are subordinate to the yellow 

 limestone f. We may therefore conclude, that the overlying conglomerates 

 in the west of England do not represent the rothe-todte-licgcnde, and that 

 they are therefore in strictness the equivalents of some of tlie higher subdi- 

 visions of the Thuringerwald system J. - - • 



6. The history of the dolomitic conglomerate in the west of England 

 certainly throws great light upon the origin of the series of deposits above 



* See Gcol. Trans. Second Series, vol. i. Part T. p. 290. f See Plate VI. figs. 2, 3. & 5. 



+ The conglomerates overlying the coal-measures near Bristol, and the conglomerates asso- 

 ciated with the transition rocks of Devonshire and Somersetshire, necessarily differ in minera- 

 logical character, but are, I believe, regarded by all geologists as contemporaneous. The con- 

 clusion of the text applies, therefore, to them all. 



A most unreasonable importance has been given to the conglomerate of Heavitree, because it 



