internal Structure of the Magnesian Limestone. 91 



they have, by the action of great disturbing forces, been broken into thousands of angular frag, 

 ments, which are in no instance water-worn, and are united by a yellow cement not differint^ in 

 texture from the earthy beds of the neighbouring cliff. In this way the ordinary deposit is here 

 and there, interrupted by great masses of breccia, in which all traces of stratification vanish. 



Proceeding southward, the complications of structure are still more striking ; for the foliated 

 the compacted, and the earthy beds are considerably contorted, and alternate with great grey 

 masses of coarse breccia. At the southern extremity of the bay, the preceding masses are replaced 

 by a system of strata in which the brecciated structure is no longer visible, the cliff being com- 

 posed of foliated, slaty, cellular, and earthy beds, alternating with thick compacted grey beds, 

 which in their weathered surfaces resemble mountain limestone. 



Near the last-mentioned point, the finely foliated structure disappears, and the earthy pulve- 

 rulent beds are less frequent. For two or three miles may be seen in a low cliff a system of slaty 

 beds (of which some parts are yellow, coarse, and cellular; other parts nearly compact, of a 

 smoke-grey colour, occasionally fetid) passing into, and alternating with, irregular masses com- 

 posed of great and small globular concretions. To the south of Whitburn, the whole cliff is com. 

 posed of these concretions, varying from a quarter of an inch to a foot and a half in diameter : 

 but, before reaching the banks of the Wear, they are replaced by a regularly bedded yellowish 

 white magnesian limestone of earthy texture. 



In a part of the coast between Castle Eden-dean and the sands to the north of Hartlepool, we 

 find the same complications of structure, the same brecciated beds and globular concretions, and 

 the same passages from one modification into another ; and, as a natural consequence, the cliff 

 has, by the action of the waters, been worn down into the same kind of grotesque forms and 

 great insulated masses which were before remarked in Marsden bay. Here, however, the earthy 

 structure is more prevalent ; and the finely foliated beds above described are represented by a 

 series of fetid beds, generally of a dark brown or smoke-grey colour and slaty texture*. Moreover, 

 the contortions are more violent, and the subordination of the brecciated masses to the other beds 

 is more distinctly exhibited than at Marsden rocks ; for not only in the cliff, but also in the great 

 perforated masses which are surrounded by the waters, we find the breccias distinctly surmounted 

 by regular brown, slaty, or foliated beds, associated with yellow, cellular, amorphous, concre- 

 tionary masses. 



These details may convey some notion of the complex and irregular structure of the whole de- 

 posit, which can be seen in no place so well as in an extensive coast section f. Thoy also seemed 

 necessary to an explanation of the true relations of the brecciated masses. 



It appears then, that these breccias are neither at the bottom nor at the top 

 of the formation of mag-nesian limestone, but that they are subordinate to it; 



* In one or two places, the earthy incoherent masses, when rubbed or struck with a hammer, 

 are as fetid as the regular beds with which they are associated. 



t Many of the natural sections in the ravines M'hich are transverse to the formation of mag- 

 nesian limestone illustrate the same fact. For example, the clifl's on both sides of the Nid near 

 Knaresborough exhibit some fine modifications of magnesian limestone ; but the different varieties 

 replace each other with so little regularity, that in many places it is not possible to find the cor- 

 responding points of the sections on the opposite sides of the river, though its direction is trans- 

 verse to the bearing of the strata. A confirmation of this fact may sometimes be seen even on the 

 opposite sides of a narrow cut, made through the beds of the deposit for the passage of the public 

 road. 



n2 



