and Freshwater Deposits of Eastern Norfolk. 377 



to attribute the bendings, inclination, and dislocation of strata; 

 secondly, by landslips or the sliding down of sea-cliffs, or the 

 falling in of undermined banks of rivers or of submarine 

 sand banks; thirdly, by the stranding of islands and bergs of 

 ice. It is possible that all these three causes of disturbance 

 may have co-operated to produce the complicated movements 

 which we now behold in the cliffs under consideration. 



Bi/ ordinarij subterranean movement, — First, in regard to 

 ordinary subterranean movements, a general subsidence must, 

 I conceive, have taken place over a considerable area, in order 

 to explain the submergence and burial of the trees of which 

 the stools are found in situ ; and this forest bed could not 

 have been brought up again, together with the incumbent 

 drift, to the level of low water, without a subsequent upheaval 

 nearly equal in amount to the previous subsidence. But 

 such a depression and re-elevation of a large tract may have 

 taken place slowly and insensibly, and without any derange- 

 ment of the stratification, A question would still remain, 

 whether such protuberances of chalk as those at Trimming- 

 ham (p. 357), and the inclination or verticality of the asso- 

 ciated drift, should be attributed to a local and violent move- 

 ment from below, fracturing the chalk and thrusting up 

 portions of it above the ordinary level of that formation. It 

 is scarcely profitable to speculate on a subject which could 

 only be set at rest if the section were prolonged downwards 

 into the subjacent chalk. I have described in the Geol. 

 Trans., vol. v., part 1, p. 243, masses of drift entangled in 

 chalk at the top of the cliffs of Moen in Denmark; but in 

 those lofty cliffs the section extends downwards for a depth 

 of more than 400 feet into the underlying chalk with flints. 

 The verticality of some of the layers of flint, the curvature of 

 others, and numerous faults, bear testimony to such repeated 

 convulsions, that I did not hesitate to refer tlie entanglement of 

 the upper chalk and incumbent drift of Moen to subterranean 

 movements. During those convulsions, fissures and chasms 

 may have opened in the chalk, and masses of the superimposed 

 boulder formation may have been engulfed. 



There are many sections^ such as that represented in fig. 14, 

 p. 368, where the first hypothesis which suggests itself is the 

 protrusion upwards of a boss of chalk, which has forced the 

 yielding and incumbent beds to fold round it, so that the beds 

 become peifectly vertical on the flanks of the protuberant 

 chalk. But it fiequently happens that these masses repose on 

 chalk and crag so horizontal and undisturbed, that we are 

 entirely precluded from the supposition of a movement from 

 below upwards. 



Fhil Mag, H, 3. Vol. 16. No, 104. i\f«j/ 1840. 2 C 



