Ill] GEOLOGICAL EVOLUTION. 53 



and gravel long known under the name of 'Crag.' The beds 

 have a very modern aspect ; the sands have not been converted 

 into sandstones, and the shells have undergone but little change. 

 These materials were for the most part accumulated on the 

 bed of a shallow sea which swept over a portion of East Anglia 

 in Pliocene times. In the sediments of this age northern forms 

 of shells and other organisms make their appearance, and in 

 the Cromer forest-bed there occur portions of drifted trees with 

 sands, clays and gravels, representing in all probability the 

 debris thrown down on the banks of an ancient river. At this 

 time the greater part of the North Sea was probably a low- 

 lying forest-covered region, through which flowed the waters of 

 a large river, of which part still exists in the modern Rhine. 

 The lowering of temperature which became distinctly pro- 

 nounced in the Pliocene age, continued until the greater part 

 of Britain and north Europe experienced a glacial period, and 

 such conditions obtained as we find to-day in ice-covered 

 Greenland. Finally the ice-sheet melted, the local glaciers of 

 North Wales, the English Lake district and other hilly regions, 

 retreated, and after repeated alterations in level, the land of 

 Great Britain assumed its modern form. The submerged 

 forests and peat beds familiar in many parts of the coast, the 

 diatomaceous deposits of dried up lakes, "remain as the very 

 finger touches of the last geological change." 



The agents of change and geological evolution, which we 

 have passed in brief review, are still constantly at work carrying 

 one step further the history of the earth. A superficial review 

 of geological history gives us an impression of recurring and 

 wide-spread convulsions, and rapidly effected revolutions in 

 organic life and geographical conditions ; on the other hand a 

 closer comparison of the past and present, with due allowance 

 for the enormous period of time represented by the records 

 of the rocks, helps us to realise the continuity of geological 

 evolution. '* So that within the whole of the immense period 

 indicated by the fossiliferous stratified rocks, there is assuredly 

 not the slightest proof of any break in the uniformity of 

 Nature's operations, no indication that events have followed 

 other than a clear and orderly sequenced" 

 1 Huxley (93), p. 27. 



