My dear Darwin

Many thanks for your orchid book which I received some time ago & have been carrying about with me in hopes of being able to read it.¹ Hitherto I have only dipped into it and it seems excessively interesting.— Field work and reading are I find almost incompatible, after a blow on the hills, or as yesterday a climb about a mine, one has such a fatal facility for falling asleep after dinner if one attempts to read, that one is off into the land of nod without being aware of it & though I am an early bird yet I find letters, geological notes &c &c take all ones time before breakfast.—

While you are working away at the Organics I am chiefly laying the physical substratum for future observers to work on. I have however hit upon one conclusion lately which I think will interest you.—

Many of the rivers of Ireland after running over a low limestone plain with water sheds not exceeding 300 feet, escape to the sea by deep gorges thro’ hills of Slate & Old Red &c more than double that height.—

Some in the S. after running down long limestone valleys between ORS² ridges, those valleys & ridges running straight out to the sea with same features, suddenly turn from the valleys & run through deep transverse ravines across the ridges. These latter cases I have been enabled to link on to some lateral brooks coming down from the loftier ridges on the N opposite the points where the transverse ravines commence & to show that the ravines were formed by these brooks, being commenced on a higher surface & always cutting down by running water faster than the surface of the valleys sank. Therefore it was always dry land & the valleys have been worn by atmospheric degradation alone.—³ The Limestone has in fact been dissolved; & the limestone plains & valleys have lowered & sunk down past the other rocks like glaciers sinking in their beds under a hot sun.

The other rocks have also suffered by atmospheric degradation valleys being worn in the softer parts of them.

Supposing my explanation be right in Ireland it must be applicable elsewhere. The Weald for instance, which after all is a mere flea bite compared to the denudation of the Palæozoic rocks.— I suspect that the Chalk was bared of the Tertiary rocks by marine denudation as the rock rose above the Sea, that brooks commenced to run down the chalk slopes along the courses of those which now cut ravines through the Chalk escarpments, & that those ravines have been worn by those brooks continually cutting deeper than the ground inside, that the Chalk which has been removed has been merely dissolved off the crown of the arch by atmospheric action & the hills & valleys inside worn by the rain only & the weather. Your 300,000,000 of years is not nearly enough for the denudation of the Weald by this process.⁴

I have sent in a paper to the Geol: Soc: Lond: on the Irish valleys w.^h is to be read on June 18^th.—⁵

I intend to be there with large maps and sections and I shall be anxious to hear if any one can pick a hole in the reasoning or give another explanation for the phenomenon

I have long been considering the “Form of Ground” as a geological problem as yet unsolved and think my idea will give us a help.—⁶

Agrarian outrages beginning to sprout again all over this Tipperary country.—⁷ Much wider emigration wanted. Only fancy! I was told by Cap^tn. King at Silvermines yesterday, that one man had given another £80 for the possession of 6 acres of land on the hill side there: both being mere tenants at will of Lord Dunally’s.⁸ When the peasants buy the land in this way from one another no wonder they fancy it is their own.⁹

Believe me | yours very truly | J. Beete Jukes.