While referring the present “form of the ground,” in a large degree, to the several agencies of atmospheric and marine denudation, do not let us ignore the, at least, equally efficacious action of subterranean force. This Professor Jukes appears to me to do, to an extent likely to mislead ordinary readers, naturally influenced by his high authority, in the communication from him published in your last number (Vol. III. p. 232). He there speaks of “the action of internal forces,” as “having no direct effect on the external features of the ground.” In a subsequent sentence, indeed, he makes exception, in a parenthesis, of “volcanic cones and craters,” but seemsto consider these exceptional cases as of trifling moment, and to deny altogether the influence of other internal forces in producing superficial elevations or depressions.