To Daniel Mackintosh   13 November 1880

Dear Sir.

Your discovery is a very interesting one & I congratulate you on it.¹ I failed to find Shells on Moel Tryfan, but was interested by finding (Philosoph Mag. 3^rd. Series— Vol XXI p. 184) shattered rocks & far distant rounded boulders, which I attributed to the violent impact of icebergs or coast-ice—² I can offer no opinion on whether the more recent changes of level in England were or were not accompanied by earthquakes.— It does not seem to me a correct expression (which you use probably from haste in in your note) to speak of elevations or depressions as caused by earthquakes;— I suppose that everyone admits that an earthquake is merely the vibration from the fractured crust when it yields to an upward or downward force— I must confess that of late years I have often begun to suspect (Especially when I think of the step-like plains of Patagonia, the heights of which were measured by me). that many of the changes of level in the land are due to changes of level in the sea.³ I suppose that there can be no doubt that when there was much ice piled up in the Arctic Regions the sea would be attracted to them, and the land on the temperate regions would thus appear to have risen   There would also be some lowering of the sea by evaporation and the fixing of the water as ice near the Pole—

I shall read your paper with much interest when published | & remain | Dear Sir. | Yours faithfully. | Ch. Darwin.