In replying to Mr. Forbes” strictures upon my paper at Cambridge upon “The elevation of Mountains, etc,” I may be permitted to say, what would otherwise be of no consequence. The paper was read in April 1868. I received it back from the referees, accompanied by some valuable suggestions, in September. I was at that time much occupied, and did not work out those suggestions until January 1869. After having done so I wrote to Mr. Forbes, received his reply on the 29th, and a week later sent the paper back to the referees.