550 



Fisher — Denudations, of Norfolk. 



around the area invaded by the foreign mass.^ This will, I believe, explain many 

 of the anomalies of what has been called the contorted Drift. Wherever con- 

 siderable contortions occur, they will be fovmd connected with the dropping of a 

 mass of sand, or gravel, or chalk, or of some matter differing from the stratified 

 clay which is thrown into contortions. When the mass is very large, it sometimes 

 has sunk down through, not only the upper but also the lower part of the lower 

 Boulder-clay, and in one case I noticed that it had deranged the horizontality of 

 the laminated beds beneath. 



a. a. Two masses of Gravelly sand dropped upon the Lower Boulder-clay, pressing it to the 

 right and left, and contorting even the laminated beds [b], which are very seldom 

 affected in that way. Cliff between 30 and 40 feet high. 



Very often the mass which has fallen has evidently been at the time frozen, so 

 that its parts have maintained positions which they could not otherwise have pre- 

 served. For instance, I noticed one mass in which was a piece of ripple-marked 

 mud, its surface in a vertical position, and the ripple marks at an angle of about 

 75° to the horizon. Nothing is more common than to meet with patches of shelly 

 sand in all kinds of positions inexplicable on any other supposition than that they 

 were solid masses at the time they fell. Now that such a case may happen is not 

 only possible but certain. If a frozen mass, consisting of ice and rock, whether in 

 the form of sand, clay, gravel, or stone, be just capable of floating, the earthy 

 matter cannot exceed about one-twentieth in bulk of the whole mass.^ The 

 moment that, by the thawing of the ice, the ratio of rock to ice exceeds this, the 

 whole must immediately sink. It is true that we may conceive the rock to be so 

 arranged in the berg that it might all be liberated without the berg sinking, but in 

 the infinite number of ways in which the rocky matter may happen to be distributed, 

 it cannot but occur that blocks of ice containing earthy matter must usually 

 sink before they are thawed. 



Thus, Mr. Trimmer's supposition is established, that ice may have become em- 

 bedded in the sea bottom, and, by its subsequent liquefaction, may have contributed 

 to produce the contortions.-^ I believe, however, that the principal cause was that 

 previously described. 



In attributing contortions in the underlying beds to the deposition of masses of 

 matter upon their surface, I would go to the extent of suggesting that the remark- 

 able bluffs of chalk at Trimmingham may have been upraised by some such action. 

 There are two of these about half a mile distant from each other. The shore be- 



* See Lyell's Principles, Vol. I., 1867, p, 447. 

 2 / the volume of ice in the berg. 

 M ,, ,, stony matter, 



^vol. of water displaced. 



6" the specific gravity of ice = -92. 

 S' ,, ,, of granite for stony matter = 2 '5. 



I ,, ,, of Water. 



Then because the mass floats S / + S' M = i W, and because it is on the point of sinking 

 that it has no part above water, I -\- M^ W. 



J - ^'—'^ _ U, 



M ~ " 



I — S -08 



TT M Stony matter 



/ + M whole mass 



: 19 nearly. 

 = — nearly. 



Journ. Geol. Soc, vol. vii. p. 22. 



