The proofs of a much greater elevation of the American continent at no very distant geological date, which have been communicated to the Geol. Mag. by Prof. J. W. Spencer and Mr. W. Upham, are very interesting, and Mr. Upham's suggestion that this great elevation occurred in Pliocene and early Pleistocene time is a taking one. He thinks the culmination of the uplift coincided with the Glacial period, and was to a large extent the cause of that period; if he is right, we are forced to infer that there has been a post-Glacial submergence to the extent of over 3000 feet over the whole region, including the Gulf of Mexico. There is, however, a difficulty in this supposition, to which I beg to call Mr. Upham's attention.