S52 Mr. Lyell on the Bonldei' Formation, 



horizontal beds, and apparently the till also, of which the sur- 

 face is so even, have not participated in these movements even 

 in the smallest degree, we are compelled to suppose that some 

 lateral force has been exerted against the upper masses of 

 drift which has not been applied to the lower ones. Yielding 

 beds having a thickness of at least 15 or 20 feet must in some 

 cases have been subjected to this sideway pressure and moved 

 bodily ; and it is impossible to conceive that any original irre- 

 gularity in the mode of deposition, nor any shrinking or set- 

 tling of the materials, nor anything in short but mechanical 

 violence, could have produced such complicated folds. Com- 

 monly we are in the habit of attributing such movements to 

 a subterranean force acting from below, but it is difficult to 

 imagine how such agency could have disturbed the overlying 

 beds without affecting the subjacent. I shall defer to the se- 

 quel the consideration of the various hypotheses which may 

 be suggested to account for such appearances, first describing 

 other irregularities and apparent anomalies which present 

 themselves in this same line of cliffs. 



At one spot between Bacton and Mundesley, where the 

 cliff' is 50 feet high, I observed at a depth of 30 feet from the 

 top, a small pit or furrow as it were cut into strata of blue 

 clay, and filled with fragmentary white chalk and chalk flint, 

 regular strata of sand and loam being superimposed. This 

 indentation was four feet deep and six wide, and precisely 

 resembles those irregularities which we see in superficial 

 gravel ; and they may all be explained if we suppose, that 

 during the subsidence which is indicated by the buried forest, 

 the drift of the mud cliff's was formed in very shallow water, 

 so as to be exposed to the denudation of small streams or 

 currents, by which narrow grooves and hollows were exca- 

 vated, then filled with drift, and then, after the sinking of the 

 whole, overspread with regular strata. 



Fresh-water Strata at Mundesley. — Both to the north and 

 south of Mundesley, the cliff's, varying in general from 40 to 

 70 feet in height, consist in their lower part of blue clay or 

 till, covered with stratified yellow sand and loam ; but at the 

 town of Mundesley itself the cliff' lowers to a height of be- 

 tween 20 and 30 feet, and for several hundred yards is occu- 

 pied by a freshwater deposit, covered with about 10 feet of 

 ffint gravel. The fresljwater beds consist of brown, black, 

 and grey sand and loam, mixed with vegetable matter, some- 

 times almost passing into a kind of peaty earth containing 

 much pyrites. A few layers also of gravel occur composed 

 of rounded flint pebbles. These beds are often irregular and 

 rarely continuous for great distances. The bottom of the de- 



