preserved in it prove that in the first instance it must have grown at the rate of about three feet in a century, and after the destruction of the forest its rate of increase down to the present time diminished rapidly almost to nothing. Its age is thus reduced to perhaps less then 4000 years. In 1865 I had an opportunity to examine the now celebrated gravels of St. Acheul, on the Somme, by some supposed to go back to a very ancient period. With the papers of Prestwich and other able observers in my hand, I could conclude merely that the undisturbed gravels were older then the Roman period, but how much older only detailed topographical surveys could prove; and that taking into account the probabilities of a different level of the land, a wooded condition of the country, a greater rainfall, and a glacial filling of the Somme valley with clay and stones subsequently cut out by running water the gravels could scarcely be older then the Abbeville peat. To have published such views in England would have been simply to have delivered myself into the hands of the Philistines. I therefore contented myself with recording my opinion in Canada. Tylor[AO] and Andrews[AP] have, however, I think, subsequently shown that my impressions were correct. In like manner, I fail to perceive, and I think all American geologists acquainted with the pre-historic monuments of the western continent must agree with me, any evidence of great antiquity in the caves of Belgium and England, the kitchen-middens of Denmark, the rock-shelters of France, the lake habitations of Switzerland. At the same time, I would disclaim all attempt to resolve their dates into precise terms of years. I may merely add, that the elaborate and careful observations of Dr. Andrews on the raised beaches of Lake Michigan, observations of a much more precise character then any which, in so far as I know, have been made of such deposits in Europe, enable him to calculate the time which has elapsed since North America rose out of the waters of the Glacial period as between 5500 and 7500 years. This fixes at least the possible duration of the human period in North America, though I believe there are other lines of evidence which, would reduce the residence of man in America to a much shorter time. Longer periods have, it is true, been deduced from the delta of the Mississippi and the gorge of Niagara; but the deposits of the former have been found by Hilgard to be in great part marine, and the excavation of the latter began at a period probably long Anterior to the advent of man. [AN] "Transactions, Chicago Academy," 1871. [AO] "Journal of Geological Society," vol. xxv. [AP] "Silliman's Journal," 1868.