AUGUST 193 



proved can exist in extreme polar cold. ' First,' says 

 Sir Archibald Geikie, 'there was a gradual increase 

 of the cold, though with warm intervals, until the 

 conditions of modern North Greenland extended as far 

 south as Middlesex, Wales, the south-west of Ireland, 

 and 50° N. latitude in Central Europe.'^ In other 

 words, the greater part of Britain lay for an unknown 

 period under land ice thousands of feet thick, just as 

 North Greenland lies at the present time. The ice-field 

 does not appear to have extended south of the Thames, 

 but it has left evidence of its presence as far south as 

 that river, which was probably frozen solid every 

 winter, and even if the brief summer prevailed to set 

 it running again, the current must have been ice cold 

 and thickly charged with glacial mud. That being so, 

 it seems impossible that any fish can have survived in 

 the Thames or in any of the easterly flowing rivers 

 north of it. During the period of extreme cold a vast 

 ice-field must have occupied the plain now covered by 

 the North Sea, forming a continuous sheet extending 

 from Scandinavia to what is now Great Britain. It 

 was explained by the late Mr. Clement Keid that a 

 barrier was thereby created through which the Rhine, 

 powerful river though it was, could not force a passage. ^ 

 It would simply add bulk to the barrier by its own 

 waters freezing as fast as they reached the region of 

 intense cold. The result of this great dam would be 

 the formation of a huge lake, which found its outlet 

 through what is now the Straits of Dover and flowed 



1 Text-book of Geology, p. 884. 



' Submerged Forest), by Clement Reid, 1913, 



N 



