90 Rev. A. Sedgwick on the Geological Relations and 



limestone exhibiting- beautiful shades of yellow, red, and brownish-red colours, 

 which are found on the east side of Bramham Moor, and in some quarries 

 near Newton Kyme : also some large beds of bright-yellow dendritic crystal- 

 line limestone, which appear in the cliiF on the left bank of the Nid, about a 

 mile and a half below Knarcsborough. In these instances, the composition of 

 the rock does not seem to be due to any separation of parts after deposition. 

 It has tiie external characters of dolomite, yet it contains only a mere trace of 

 magnesia : it may therefore be regarded as an extreme (and in this part of the 

 formation a very rare) case of magnesian limestone, in which the triple salt 

 has almost disappeared *. 



VIII. Rocks of a brecciated structure, Sgc. — The obscure bands of conglo- 

 merate which in a few places separate the magnesian limestone from the 

 lower red sandstone, do not, either from their thickness or continuity, deserve 

 any detailed description; and were only mentioned above (p. 74.) because 

 they seemed to have originated in those causes which produced a local want 

 of conformity between the inferior and superior deposits. There are, how- 

 ever, in other places (especially on the coast of Durham) great beds of a coarse 

 brecciated structure, which cannot be passed over without some notice : and 

 they may be properly introduced in this place, because they occupy the same 

 part of tiie series as the irregular concretionary rocks above described, and 

 sometimes seem to pass into them by gradations which are almost imper- 

 ceptible. 



Commencing an examination of the coast of Durham at North Point, about two miles south of 

 the Tyne, we find a lofty cliff composed of a brown-coloured marl. slate, sometimes coarse and 

 cellular, surmounted by grey-coloured cellular amorphous masses of large irregular concretionary 

 structure. This is the general character of the coast for more than a mile. To the north of 

 Marsden Bay (a place celebrated for the great picturesque masses of insulated rock which have 

 been formed by the irregular encroachment of the sea upon the neighbouring cliff), the whole 

 escarpment is composed of a hard grey cellular rock, with many knotty protuberances. But 

 further south, on entering the bay, the preceding modification is gradually replaced by a system 

 of beds which are partially fetid, are of a yellowish brown or buff colour, of a slaty and finely 

 foliated structure, and which occupy a cliff more than one hundred feet high. The foliations 

 often alternate with soft earthy laminae, giving the weathered surface of the rock a striped or 

 grooved appearance. These beds in turn exhibit various modifications ; some portions contain 

 cells with spheroidal concretions ; others lose their foliated texture, and pass into irregular yellow 

 earthy masses, alternating with harder compacted greyish bedsf. After some slight undulations 



* In the above remarks it is taken for granted, that, in this formation, carbonate of magnesia 

 appears only in chemical combination with carbonate of lime. This is undoubtedly the general 

 fact ; but the rule perhaps admits of some exceptions. 



t In this part of the coast it is not perhaps possible to determine the true relations of all the 

 beds. Some of the foliated masses may represent the " marl-slate" of the preceding section. (§ 2. 

 p. 75.) The greater portion of them are, however, in a higher position, and belong to the modi- 

 fication described above. (No. IV. p. 86.) 



