34

Feb 22/72

Worms

Dr Forbes says he has good reason for believing that changes of temperature not only the sun even deep down, owing to percolation of water has important influence of disintegration. — Water with carb acid not only removes matter, but combine & form new minerals (not yet published) & exerts purpose by expansion. Agrees about frost & Tropics — Agrees that fragment in bath of water & carbonic acid more acted on the freely exposed rocks — Proved that it is not ammonia which acts on glass — In thick silex in 2 states, in one soluble in plain water; so that water alone has more power of disintegration than wd be expected — Many angular fragments of chalk are rounded owing to point being over exposed on each sides to the action of moisture.

Says he has seen on mountain of Norway Hemline wrinkles, where there are no sheep. 

[in margin:] On disintegration of rocks

[David Forbes (1828-1876) was a mineralogist and geologist. This records a conversation during Darwin's stay in London in February and March 1872. Darwin mentioned some of these details in a letter to his brother on [1 March 1872] , Correspondence vol. 20, p. 94.]

34v

roots exerting Carbonic acid wd be dissolved