Geology of the Neighbourhood of Weymouth, Sf c. 7 



irreo-ularities which exist below : but however rug-ged be the subjacent surface 

 of the chalk, its irregularities are all obliterated and filled up with breccias 

 and gravel beds, presenting on their upper surface a smooth and continuous 

 outline, whilst their lower surface is curved and dentated downwards, con- 

 formably to the furrowed curvatures, and ridges and pinnacles that fringe the 

 upper surface of the chalk on which they rest ; the existence of these pits 

 and cavities shows, that the chalk had not been exposed to the levelling- 

 effects of atmospheric agents before the deposition of these breccias and 

 gravel beds. 



The water which formed these breccias must have been subject to very irre- 

 gular currents and agitations ; for whilst in many places (such as those last 

 mentioned) the solution has been conducted in perfect tranquillity, in other 

 spots it has been attended or followed by agitations which have reduced the 

 flints to perfect roundness, as in the Hertfordshire pudding-stone and Black- 

 heath gravel ; and again, in other cases, there is evidence of an intermediate 

 state of action, where only a partial rounding of the fragments has taken 

 place, as in the partly rounded and partly angular chalk flints which form a 

 thick bed reposing on strata of greensand on the summit of Haldon, on the 

 west of Exeter. 



Another variety of angular gravel occurs in many beds of shivered chert of 

 the greensand formation, which seem to have undergone a certain degree of 

 decomposition, causing them entirely to break to pieces and crack into angular 

 fragments, and become converted into strata of loose and shivered gravel, on 

 which no mechanical attrition seems to have been produced by the operation 

 of water, but the fractures have resulted from the splitting to pieces of the 

 beds of chert still resting in their natural position. A remarkable example 

 of this kind may be seen in the cliffs that overhang the new road between 

 Lyme and Charmouth, and also on the summit of Abbotsbury Castle. In 

 the oolite formation also, about two miles west of Bridport, a similar dislo- 

 cation and splitting of the stone has converted to loose breccia the upper beds 

 of inferior oolite on part of the summit of Chideock Hill. This is the only case 

 we have noticed of such an occurrence in the oolite of the coast of Dorset. 



It is not easy to distinguish between these undisturbed beds of shivered chert, 

 and accumulations of the same chert which have been very slightly agitated 

 by water, except in cases where the admixture of miscellaneous fragments of 

 other strata shows that moving water has operated in bringing these frag- 

 ments to their present position amongst the chert. There is also a difficulty 

 in distinguishing the deposits of angular breccia, both of this chert and of 

 the chalk formation, from deposits of diluvial gravel which have been removed 



