It was in 1903 that the writer printed his first paleogeographic map, and seven years later that the Geological Society of America did him the great honor of publishing fifty-two such maps of North America. Since then, as stratigraphers have brought to light new data, today from Alaska and tomorrow, perhaps, from Mexico, these maps have been altered to record the new finds, and their number has increased until they now represent one hundred and fifteen formations, beginning with the earliest Cambrian. It is, therefore, a pleasure for the writer to bring before the same Society that fourteen years ago listened to the initial presentation of these North American maps the broader conclusions that have crystallized out of their study during the intervening years.

The synthesis of my studies may be expressed in the words of another presidential address, namely, that of Le Conte, given in 1897.2 Nearly all . . .

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