GEOLOGY. 247 



to the sea-raargin, that the trees had died, and that mud-deposits 

 had formed, partly under fresh, partly under brackish water la- 

 goons. Subjacent to the " Forest-l)ed," and covering the surface 

 of the chalk, is a layer of chalk flints ; a like accumulation is seen 

 resting on the chalk in numerous other places, as in the sections 

 below this city, and are all referable to the same agency and period. 

 The flints have been dissolved out of the chalk by the action of 

 rain-water, and left in situ; they indicate a long period of sub- 

 aerial conditions; and their formation is coextensive with the 

 whole duration of those conditions ; they are, therefore, of the 

 same period as the ''Forest-bed." Glacial. — More recently the 

 Norwich sections have been subjected to a closer examination ; 

 and, according to Mr. J. E. Taylor, these admit of a two-fold 

 division : the upper is a coarse and rubbly accumulation, with 

 well-rounded pebbles of flint; the lower consists of finer sands. 

 A band of white cross-bedded sand intervenes. Such a change 

 in the character of successive beds would not, by itself, have been 

 of much importance ; but zoologically the differences they present 

 are much more significant. 



The Rev. Osborn Fisher, in an elaborate paper "On the Denu- 

 dations of Norfolk," called attention to the denudations upon the 

 land surface, stating that a certain amount of the fine material 

 was being carried into the rivers, and by them deposited at the 

 heads of the broads or in the sea. This denudation, by pluvial 

 action, was undoubtedly greater where the land was under the 

 plough than it would be otherwise. Upon the coast, the sea was 

 reducing the solid surface ta a uniform level. Where the land 

 was high it cut away the bottoms of the cliffs, which then foun- 

 dered down, and the fallen matter was in its turn carried off, and 

 where it was low, the general contour of the coast was being con- 

 tinued by sand dunes or *' Marram Hills," so that where the lower 

 end of a valley was submerged, its bottom was being raised sea- 

 ward, and reduced to a uniform level and continuous coast-line. 

 But when the waves had played their part the action of the sea 

 was not ended. As the sea cut further into the sand the ground 

 laid under water became subject to the action of tides, so as to be 

 kept on the whole at a uniform dej)th for a given distance from 

 land. If the waste of the shore was prevented by artificial means, 

 the sea was found to deepen rapidly, and the inclination of the 

 bottom from the shore to be increased. This marine action, if 

 considered, did not appear possible to give rise to any very great 

 inequality of surface, but, on the other hand, it must tend to re- 

 duce those already existing. All great inequalities of the sea-bot- 

 tom must either have been caused by the land having become 

 submerged more rapidly than the sea had time to move its coast- 

 line, or else by elevations and depressions taking place beneath 

 the ocean, or, in a few instances, by powerful currents confined 

 by local circumstances to a narrow course. Since the tides deepen 

 the sea below the level to which the waves acted upon the coast, 

 it must follow that the harder rocks would be lowered more slowly 

 than softer, and shoals be formed. It was to such a denudation 

 as just described that the form of the surface of this country might 



