74 



that is to say at a period when there is at present no satisfactory 

 evidence that man had yet reached Britain. 



You will naturally ask how this restoration of the boundaries of 

 land and sea is arrived at , when the evidence has been so completely 

 swept away, as is shown east of the Isle of Wight, where the 

 whole of the southern side of the old valley has now completely 

 disappeared. Various lines of research led to this restoration ; 

 but some of them are so complicated that it would take too much 

 time to deal with them now. We will, however, take the evidence 

 of the first glaciation in Britain, and will see what modifications 

 in the topographical features it points to in the regions with which 

 we are now dealing. 



During the Glacial Period the cold was so intense that the 

 greater part of Britain was smothered under ice and snow. Even 

 in these southern latitudes around Bournemouth the cold was so 

 great that the seas were blocked in winter by floe-ice, and the soil 

 was deeply frozen. There were no towering icebergs here during 

 the greatest intensity of the cold ; for though the climate was so 

 cold, no glaciers reached the sea on the borders of the English 

 Channel. 



To realize clearly what it was like in the South of England, 

 a few words more are necessary as to what happened there. In 

 order to understand our valleys we must first grasp the climatic 

 changes which so greatly influenced their formation. This is all 

 the more necessary because some of the most striking evidence 

 has not yet found its way into the geological text-books. Indeed, 

 naturalists in this country have as yet little conception how greatly 

 conditions were modified for a time, or how sweeping were the 

 changes in the fauna and flora. Geographers also scarcely 

 understand the greatly increased rate of erosion which was then in 

 progress, or the peculiar modifications of the processes of erosion 

 caused by the cold. 



Try and imagine what it must have been like when the climate 

 was about 20 degrees colder than now. Many years ago I made 

 an isothermal map of NW. Europe, but if anything the degree of 

 cold was somewhat underestimated, however, I here reproduce it 

 on page 75. On this map the line showing a mean annual 

 temperature below the freezing point is found far to the south, 

 and passes through London. With such a climate, an 

 Arctic vegetation must have clothed the whole of the south of 

 England. As a matter of fact, many Arctic plants have 

 been found fossil in the Lea Valley, close to London, 

 and the dwarf Arctic birch has been found as far west 

 as Bovey Tracey, in Devon, in one of the hottest valleys in Britain. 

 Unfortunately we have not yet discovered this Arctic flora near 

 Bournemouth, and it is one of the things still to be searched for. 



As regards the fauna we are more fortunate, for only a few 

 miles away, in the suburbs of Salisbury, a thoroughly Arctic 

 fauna has been found, including reindeer, musk-ox, Arctic-fox, 

 lemming, and many others. 



