The cause of the formation of mountains is so difficult and so vast a question that I cannot undertake to answer all Captain Hutton's objections to what he concisely calls the “contraction” theory. Moreover, I feel that, as far as my endeavours can help to elucidate so great a subject, I shall do better to throw what I have further to say into a form which is not controversial. I desire not to be held a champion of any theory, and shall always honestly abandon any position, which subsequent consideration leads me to think untenable. Thus with respect to paragraph (7), p. 26, in Captain Hutton's rejoinder to my critique, I refer to the abstract I have sent to the Magazine of my paper lately read at Cambridge, for it supersedes some of the purely tentative suppositions to which Captain Hutton takes exception, and which I adopted six years ago as “not unreasonable,” in order to test the application of the theory.