To Leonard Horner 27 April 
Down Farnborough Kent
My dear Mr Horner
I was regretting a year ago that I had not published a fuller account of the superficial beds,1 which I cd. have done from my M.S. but not being able to give any explanation, I cut the very little which I had to say to one paragraph at p. 143 of my Geolog. Obser. on Volcanic Isld.—2 I see I have not used the word vitrified, but I often have in conversation. I stated to you that one officer described the appearance as a stream of lava.— Another on coast of Australia said that the whole country seemed to have been fused by a flash of Lightning. These expressions will show what the appearance is.— You will see that my cases are in contact with Granite.— Rely on it, there is not, as Haidinger says, anything on earth to do with Heat.3
Pray forgive this hurried note: for it has chanced I have had to write several this morning.—
Believe me | My dear Mr. Horner | Yours very sincerely | C. Darwin
Regrets that he has not published his information on superficial beds except in abbreviated form, on p. 143 of Volcanic islands.