The maximum thickness of the North American Devonian seems to be about 15,000 feet in the northern Appalachian region, but elsewhere it generally ranges from 1,000 to 4,000 feet thick. In North America the subdivisions of the Devonian strata of New York are taken as a standard for comparison, both because of the wonderful completeness and almost undisturbed character of the rocks there, and because they have been so carefully studied. The Devonian system is there fully 4,000 feet thick, with scarcely a minor subdivision missing, and it covers a wide area (one-third of the State) with many excellent outcrops. There was practically uninterrupted deposition of Devonian strata in southern New York. It is doubtful if there is greater refinement of knowledge regarding the Devonian or any other Paleozoic system of strata anywhere else in North America. During middle to late Devonian time the region from southern New England to Nova Scotia and the St. Lawrence Valley was notably disturbed by earth movements, the lands having been considerably elevated and the rocks more or less folded. The great delta deposit of late Devonian time, already described as being thousands of feet thick in New York and Pennsylvania, was formed by one or more streams which carved much sediment from the newly upraised lands. Accompanying the uplift and folding of the rocks considerable masses of molten granite were forced into the earth's crust and some molten rock was forced to the surface, producing volcanoes. Much of the granite may now be seen at the surface in various portions of the region, while deeply eroded volcanoes occur near the city of Montreal. Except for the disturbance of the region from New England to the St. Lawrence, the Devonian period seems to have closed rather quietly, with fairly widespread sea water over the land as already outlined. This is proved by the fact that the early strata of the next period mostly rest in regular order upon the undisturbed late Devonian strata. For many years the term "Carboniferous" period was used to designate a single period of geologic time which, in America at least, is now divided into two periods--the Mississippian and Pennsylvanian--corresponding, respectively, to the earliest and latest Carboniferous. In regard to the relations of land and water during the Mississippian period, the general statement may be made that the sea, already fairly extensive in the late Devonian, continued to spread until during the second half of the Mississippian, when most of the United States west of the eastern border of the Appalachians (except the Pacific Northwest), and also the Rocky Mountain region through Canada, were submerged.