92 Rev. A. Sedgwick on the Geological Relations and 



that the disturbing forces which produced them were violent, mechanical, 

 and local, and in some instances were several times brought into action ; and 

 that they were not of long duration ; for the fragments of the beds are not 

 water-worn, and appear to have been re-cemented on the spot where they 

 were formed. 



How far these mechanical movements which broke up the half-con- 

 solidated beds during the epoch of their deposition, were connected with 

 those internal movements of the particles which, on a great scale, produced 

 the irregular concretionary structure, would perhaps be impossible to deter- 

 mine : but both causes seem in some places to have operated together; 

 for, as was before stated, we may find many large masses of an intermediate 

 character which seem to form a passage between a brecciated and a con- 

 cretionary structure. 



IX. Small concretionary structure. — Of this there are two modifications ; 

 1st, when the minute grains which enter into the composition of the rock 

 are of ill-defined and of irregular forms : 2nd, when they are better defined, 

 and are spheroidal. 



The first modification is infinitely the most abundant. In the whole range 

 of the formation we can hardly find a single cjuarry or escarpment in which 

 some of the rocks do not exhibit a dull earthy uneven fracture, and a kind of 

 compound structure ; being partly made up of minute and imperfectly gra- 

 nular portions, coated over and mixed with earthy matter which is often 

 nearly incoherent. Of this structure there are several varieties which may 

 deserve enumeration, especially as they connect the rock in question with the 

 other modifications of the magnesian limestone. 



1st. When the granulated are subordinate to the pulverulent or earthy portions. These rocks 

 have little coherence ; often soil the fingers, and pass imperceptibly into masses which are quite 

 pulverulent, like the asche of the German geologists. 



2nd. When the earthy parts are subordinate to the granulated. These rocks sometimes soil 

 the fingers ; but the harder parts cohere, and bear exposure to the weather. They are often 

 regularly bedded ; but below Knaresborough there is an escarpment nearly one hundred feet 

 high, composed of this variety, in which there is hardly a trace of stratification. In some places 

 they contain casts and other traces of organic remains. 



3rd. When the grains become very minute, and the rock passes into a nearly compact state. 



4th. When some of the granulations exhibit a glimmering lustre. The rock then begins to 

 form a passage into the dolomites above described. 



5th. When the minute amorphous grains have a dull surface, and irregularly pass into each 

 other, with a very small mixture of earthy matter. This variety, which is the most perfect ex- 

 hibition of the rock I am here describing, exists in various localities, especially in the southern 

 parts of Yorkshire, where it is met with in some places near the bottom of the formation in thick 



