1)8 EGGARDON HILL: ITS CAMP AND ITS GEOLOGY. 



past, there was certainly a time when they operated much more 

 rapidly than they do at present. When the land was at a con- 

 siderably greater height above sea level, and there was a larger 

 rainfall, the forces of denudation would act much more power- 

 fully. But there was also a period when their efficiency would 

 be increased one hundred-fold. During part of the Glacial 

 Epoch there must have been a time when the ground was frozen 

 solid to the depth of several feet, and when only a few inches 

 from the surface downwards would be thawed by the summer's 

 sun. Imagine the effect of heavy rainfall or melting snow upon 

 this squashy mud lying above ground which was frozen and, 

 therefore, impermeable to water. The mud would be simply 

 swept away. There would be no vegetation to hold it together. 

 Season after season the frost would be melted out of a fresh 

 surface, and torrents formed which would carry off the debris. 

 Some such action as this is needed to account for the moulded 

 forms of our chalk downs all over the South of England. Now 

 that they are covered with turf, and capable of absorbing the 

 rainfall like a sponge, centuries pass without appreciable change 

 in their shape. These ramparts, scarcely altered since pre- 

 historic times, are evidence of this. But there are districts, for 

 instance, in Canada, where denudation is very rapid owing to the 

 intense cold of winter followed by floods in spring acting on the 

 partially thawed surface of the ground. Anyhow, whether the 

 time required for it was long or short, the great chalk plain 

 which once extended westward from here has disappeared, and 

 the principal traces of it that still remain may be found in the 

 flint pebbles which constitute the great majority of the stones 

 upon our sea beach. If some of these pebbles could tell us their 

 whole history this would settle many vexed problems in geology. 

 But pebbles answer no questions, and we are left to find 

 " Sermons in Stones" as best we may. 



