I have seen an old boiler in action, with steam and drops of water spurting out of some of the rivet-holes. No one would think whether the rivet-holes passed through a greater or less thickness of iron, or were connected with the water higher or lower within the boiler, so small would the gravity be compared with the force of the steam. If the boiler had been not heated, then of course there would be a great difference whether the rivet-holes entered the water high or low, so that there was greater or less pressure of gravity. How to close my volcanic rivet-holes I don't know. I do not know whether you will understand what I am driving at, and it will not signify much whether you do or not. I remember in old days (I may mention the subject as we are on it) often wishing I could get you to look at continental elevations as THE phenomenon, and volcanic outbursts and tilting up of mountain chains as connected, but quite secondary, phenomena. I became deeply impressed with the truth of this view in S. America, and I do not think you hold it, or if so make it clear: the same explanation, whatever it may be, which will account for the whole coast of Chili rising, will and must apply to the volcanic action of the Cordillera, though modified no doubt by the liquefied rock coming to the surface and reaching water, and so [being] rendered explosive. To me it appears that this ought to be borne in mind in your present subject of discussion. I have written at too great length; and have amused myself if I have done you no good--so farewell. LETTER 489. TO C. LYELL. Down, July 5th [1856]. I am very much obliged for your long letter, which has interested me much; but before coming to the volcanic cosmogony I must say that I cannot gather your verdict as judge and jury (and not as advocate) on the continental extensions of late authors (489/1. See "Life and Letters," II., page 74; Letter to Lyell, June 25th, 1856: also letters in the sections of the present work devoted to Evolution and Geographical Distribution.), which I must grapple with, and which as yet strikes me as quite unphilosophical, inasmuch as such extensions must be applied to every oceanic island, if to any one, as to Madeira; and this I cannot admit, seeing that the skeletons, at least, of our continents are ancient, and seeing the geological nature of the oceanic islands themselves. Do aid me with your judgment: if I could honestly admit these great [extensions], they would do me good service.