Thanks ACR for paper and comments on it ["On the denudation of South Wales", Mem. Geol. Surv. G. B. 1 (1846): 297–335].

Sends copy of South America.

Discusses action of the sea.

Criticises ACR’s views on sudden elevation of mountain chains.

Discusses the geological origin of terraces.

Mentions R. I. Murchison’s paper ["On the superficial detritus of Sweden", Q. J. Geol. Soc. Lond. 2 (1846) pt 1: 349–81].

Comments on Tertiary beds of South America. Doubts that durable formations are now accumulating. Discusses formation of trap-rock. Notes effect of decomposition of lava; discusses action of submerged gravel on underlying rock.

Invites him to dinner on Saturday the 12th. Charles and Mrs Lyell, Edward Forbes, Richard Owen, and Thomas Bell coming also.

"Will you bring your map of S. America … and we will have a talk over it."

Asks ACR to establish height of Moel Tryfan in Caernarvonshire; "in my notice on this hill [""Ancient glaciers of Caernarvonshire"" (1842), Collected papers 1: 163–71] I give a very much less height than others". [See also another mention of the elevation of Moel Tryfan in "On the transportal of erratic boulders" (1848), Collected papers 1: 218–27.]