114 NOTES OF A NATURALIST. 



are larger than they were, but that many new ones 

 have been formed during the interval. He is satisfied 

 that the appearances, which, he admits, exactly re- 

 semble those caused by the sea on shore rocks, are 

 due to subaerial action. The chief agent, in his 

 opinion, is a cryptogamic plant growing on the surface 

 of the rock. During a great part of the year, when 

 dense fogs prevail at this elevation, the plant is in 

 active vegetation. In the alternations of relative 

 dryness and dampness of the air the cells swell and 

 mechanically remove scales from the surface, which 

 are seen to accumulate rapidly in the course of a 

 single season. 



Having submitted a specimen of the cryptogam in 

 question to the eminent lichenologist, Mr. Crombie, 

 I am informed that the plant belongs to the group of 

 lowly organized lichens, now distinguished as the 

 Epkebacei, but formerly referred to the Algce. In the 

 absence of fructification, Mr. Crombie is unable to 

 decide whether the specimen should be referred to 

 Sirosiphon or Spilonema ; but he is sceptical as to the 

 possibility of any direct chemical action upon the 

 rock arising from the growth of the lichen. Some 

 indirect action may, in his opinion, be due to reten- 

 tion of moisture on surfaces covered by the lichen. 

 This opinion is strengthened when it is remembered 

 that the rock is not affected by carbonic acid, which 

 might be derived from the air, or by vegetable acids 

 which might be formed by the decomposition of the 

 lichen. I am disposed to think that vicissitudes of 

 temperature play a great part in the disintegration of 

 rock surfaces, and such action must be increased by 



