Changes in Geography and Climate. 41 



ought to give a fairly accurate idea as to the temperature 

 of the water. No doubt a large iceberg may travel a 

 long distance through comparatively warm water before it 

 entirely melts away ; but shore-ice, such as forms every 

 winter in the Arctic Regions, once fringed our south coast, 

 and beset the shores of Brittany and of the Channel 

 Islands. When, in the spring, the ice became detached, 

 it transported its burden of included rocks hither and 

 thither, even across the Channel. We thus find on Selsea 

 Bill erratics weighing several tons, but undoubtedly derived 

 from Bognor or from the Isle of Wight, Others, equally 

 large, have come from the Channel Islands and the coast of 

 Brittany ; one block of granite is like that of Cornwall. 

 The transportation of large erratic blocks for distances of 

 at least a hundred miles, shows that the temperature of the 

 water in the spring, though sufficiently high to dislodge 

 the ice, was yet too low to melt it rapidly. Even with a 

 strong wind a flat mass of shore-ice would take several 

 days to cross the Channel. In order to compare this ice- 

 laden English Channel with existing seas, it is necessary 

 to travel northward, till we cross the isotherm of 32° P., 

 and are near the Arctic Circle. 



Thus far we ha^'e dealt solely with the temperature of 

 the sea. We will now turn to the evidence as to the 

 temperature of the air during the same period in the South 

 of England ; and for this we can employ both physical and 

 biological data. The country north of the Thames and 

 Severn, buried under ice, must have been bordered by a 

 wide strip of barren land, with dwarf birch and willow, but 

 without trees. In this belt flourished also a mammalian 

 fauna like that now inhabiting similar belts in the Arctic 

 Regions, for in the area lying between the ice-sheet and 

 the ice-cold English Channel it would be impossible to 

 have a mean temperature much above the freezing point. 



