512 



The Avon. 



heights approximately as high as the summit level of 

 the limestone gorge through which the Avon flows 

 below Bristol. 



The vulgar notion respecting the Avon and its 

 gorge is, that before that ravine was formed all the low 

 ground through which the river and its tributaries flow 

 was a large lake, that ' a convulsion of nature ' suddenly 



FIG. 103. 



Gorge of the Avon at Clifton, Bristol, looking down the river. 



rent the rocks asunder and formed the gorge through 

 which the river afterwards flowed, and so drained the 

 hypothetical lake. It is scarcely necessary to add, that 

 had there been a large lake in that area, we might 

 expect to find lacustrine deposits and organisms in some 

 parts of these valleys, but none exist. 



The true explanation is, that in some late tertiary 

 period of geological history, the surface of the country 

 on either side of the river above the gorge formed a 



