In reference to the correspondence on my speculations in theoretical geology and astronomy which have been printed in this Journal, I wish to take this opportunity of saying, that if in the cases of the Rev. O. Fisher, p. 54 in this volume, and of Dr. Leslie, p. 295 in Vol. VI., I have inserted such comments on any of the physical hypotheses to which from time to time I have given expression without replying to those comments, that I do not therefore acknowledge my opponents to be right, nor, on the other hand, do I intend to pass them over slightingly as wrong, or as unworthy of attention. I simply thought it best not to get into controversy while my own ideas were being enunciated. I cannot, however, concur in the Rev. O. Fisher's views as to the possibility of the earth's velocity, if initial primarily, being maintained, nor of a larger orbit for our planet being a result of any retardation of her motion. I am well aware of Kepler's law referred to, and I have my own opinion both of its value and its application. Mathematics may derive a result from a given basis, but mathematics never yet gave birth to a basis of facts.