Dear Sir,—

I have lately been discovering beds of rounded gravel and sand with shells on the eastern Slopes of the Welsh mountains at about the same elevation above the sea as the Moel Tryfan deposits in Caernarvonshire, and after a considerable amount of observation, I have arrived at the conclusion that there are three zones on the outer slopes of the Welsh & Pennine hills—a lower zone of rounded stones and sand with shells—then a zone of angular or subangular stones—3rd the Moel Tryfan zone of rounded gravel and sand with shells, and above it a zone of angular stones.

I am writing a paper for the Geol. Society about it, in which I have ventured to refer the angular stone zones to a comparatively rapid subsidence or elevation of the land while under the sea, or to earthquakes; and the well rounded stone zones to the sea lingering for a long time at nearly the same level.¹

You would very much oblige by letting me know if you think that in historical times the elevation or subsidence of the land has been mainly caused by earthquakes or by slow and gradual movements.

I believe that the transverse horizontality of many of the so-called raised beaches on the western coasts of Britain could only have resulted from earthquakes, and this I find is the opinion of Norwegian geologists concerning the raised beaches of their country.²

If you have written anything about the Moel Tryfan deposits would you kindly let me know.

Apologizing for troubling you with these queries, | I am Dear Sir, | Your very faithful and | obliged Servant, | D. Mackintosh.