Introduction Following the precedent of many scientific presidential addresses, I shall give a general review of one of the subjects which has occupied much of my time—the problem of the pre-Cambrian. Within an hour I can not consider the merits of the questions still in controversy, nor broadly cover the field mentioned; therefore I shall confine my review to the stratigraphy and nomenclature of the pre-Cambrian rocks. The Cambrian is defined as terminating below at the base of the well recognized Olenellus fauna. In general between the Cambrian and pre-Cambrian there is an unconformity. This unconformity for a large part of the United States is profound, being the break at the base of the great Cambrian transgression. In the early days of geology in America the name “primary” or “primitive” was given to the group of rocks under consideration. By the men who used these terms there was scarcely any . . .