any guess which would do.”  But after that it was all explained to me; and I said, “Honour to the man who has let Madam How teach him what she had been trying to teach me for fifteen years, while I was too stupid to learn it.  Now I am certain, as certain as I can be of any earthly thing, that the whole of these Windsor Forest Flats were ages ago ploughed and harrowed over and over again, by ice-floes and icebergs drifting and stranding in a shallow sea.”

And if you say, my dear child, as some people will say, that it is like building a large house upon a single brick to be sure that there was an iceberg sea here, just because I see a few curlicues in the gravel and sand—­then I must tell you that there are sometimes—­not often, but sometimes—­pages in Madam How’s book in which one single letter tells you as much as a whole chapter; in which if you find one little fact, and know what it really means, it makes you certain that a thousand other great facts have happened.  You may be astonished:  but you cannot deny your own eyes, and your own common sense.  You feel like Robinson Crusoe when, walking along the shore of his desert island, he saw for the first time the print of a man’s foot in the sand.  How it could have got there without a miracle he could not dream.  But there it was.  One footprint was as good as the footprints of a whole army would have been.  A man had been there; and more men might come.  And in fear of the savages—­and if you have read Robinson Crusoe you know how just his fears were—­he went home trembling and loaded his muskets, and barricaded his cave, and passed sleepless nights watching for the savages who might come, and who came after all.

And so there are certain footprints in geology which there is no mistaking; and the prints of the ice-plough are among them.

For instance:—­When they were trenching the new plantation close to Wellington College station, the men turned up out of the ground a great many Sarsden stones; that is, pieces of hard sugary sand, such as Stonehenge is made of.  And when I saw these I said, “I suspect these were brought here by icebergs:”  but I was not sure, and waited.  As the men dug on, they dug up a great many large flints, with bottle-green coats.  “Now,” I said, “I am sure.  For I know where these flints must have come from.”  And for reasons which would be too long to tell you here, I said, “Some time or other, icebergs have been floating northward from the Hog’s Back over Aldershot and Farnborough, and have been trying to get into the Vale of Thames by the slope at Wellington College station; and they have stranded, and dropped these flints.”  And I am so sure of that, that if I found myself out wrong after all I should be at my wit’s end; for I should know that I was wrong about a hundred things besides.