Modern Travertine of the 11 Southstone Bock," Worcestershire, from a drawing by Mrs. Murchison. 



CHAPTER XLI. 



SUPERFICIAL ACCUMULATIONS (concluded). 



Terrestrial changes within the modern sera. Desiccation of lakes and turbaries. 

 — Modern action of rivers. — Accumulations of blown sand. — Exposure of sub- 

 merged forests. — Formation of shell marl and travertine. 



Desiccation of Lakes and Turbaries. 



In the previous chapter it has been explained how certain lakes may have been drained 

 during periods antecedent to our records, though some of these bodies of water, as the 

 Wigmore Lake, appear to have been desiccated within the range of tradition. We shall 

 now treat exclusively of those operations which are entirely modern. It has been shown, 

 that the highest land occupied by the marine gravel, containing sea shells of existing 

 species, ranges from Marrington Green, north-west of Shrewsbury, to Ashley Heath, in 

 Staffordshire, and varies in height from 500 to 800 feet above the sea. From this cul- 

 minating crest, the present streams descend northwards into the estuary of the Dee and 

 Mersey, and southwards into that of the Severn. Now, as many of the minor streams 

 which rise in this crest, had a long way to flow with only a slight descent, it necessarily 

 happened, that in the early periods of our sera numerous lakes and stagnant pools were 

 formed in a surface which was then intersected with irregular depressions. Some of 



