J. W. H. Harrison 



237 



Nevertheless it must not be forgotten that a score of miles out the 

 lichens are materially influenced. How has this been brought about ? 

 The difference in the two cases, coupled with the progressive reappear- 

 ance as the towns are left behind, shows us that the deleterious agent 

 at work is the smoke, and that the apparent exaggeration of its effects 



S » Ypiipeces sordi'data 

 ft X K. ruberatoi 

 T a V- trifasciatcL 



Fells. :>:•: 



Woodland — V>';.' 

 CoaUpil- o 



Fig. 11. General map of the Team Valley. 



