94 Rev. A. Sedgwick on the Geological Relations and 



These instances are sufficient for my present purpose ; and it may be stated that even in the 

 districts where they occur, they are exceptions to the more usual character of the rock. 



In the whole range of the formation through the remaining parts of York- 

 shire to the north of the Went^ there are very few examples of an approach 

 to a decidedly oolitic structure : but it reappears in some parts of the county 

 of Durham, more particularly in the cliff on the east side of the promontory 

 of Hartlepool, where there are not less than eight or ten beds which are more 

 or less perfectly oolitic. They are associated with, and surmounted by hard^ 

 cellular, concretionary, and earthy beds belonging to several of the varieties 

 of magnesian limestone already described*. 



These various modifications of small concretionaiy structure derive a great 

 interest from the consideration, that in them are exhibited, on a minute scale, 

 the same peculiarities of aggregation, which, on a great scale, form the most 

 extraordinary features of the deposit I am describing. 



X. Large globular concretionary structure. — I have never seen a single 

 example of this structure in Derbyshire or Nottinghamshire. But it occurs, 

 though very rarely, in Yorkshire : for example, in the cliffs on the left bank 

 of the Nid below Knaresborough, associated with rocks of earthy and pulve- 

 rulent texture ; also in some quarries in the hills on the west side of the village 

 of Well. 



It is seen in its most imposing form on some parts of the coast of Durham, 

 where the whole cliff resembles a great irregular pile of cannon balls : but it 

 is not in those localities that the formation of the large spheroidal concretions 

 can be studied with greatest advantage. Their true history will be best under- 

 stood where they are associated with other modifications of the limestone. 



The following statements are the result of repeated examinations of the 

 quarries of Building Hill, Fulwell Hill, and Southwick Hill, near Sunderland ; 

 and of the coast sections, especially near Marsden Rocks and Black Rocks. 

 At all these places are found different modifications of the laminated variety 

 described above (§ 4. No. IV. p. 86.), and it is principally with them that the 

 finest concretionary masses are associated. 



1. The finest lamina are generally of a brown colour and crystalline texture ; but the beds of 

 which they are composed are often marked with a number of earthy spots on the transverse 

 surface. Sometimes these earthy marks are disposed with great regularity ; and as the matter of 

 which they are composed, not only interrupts the range of the laminas, but is easily washed out, 

 the weathered surface of the rock has, in such cases, a beautifully honeycombed appearance. This 



* This locality has often been noticed as exhibiting the finest specimens of oolite in the whole 

 range of the magnesian limestone. The spherules are, however, partly hollow and of earthy 

 texture ; and so much mixed with earthy incoherent matter, that very few of the beds in question 

 would afford a good material for building. 



