In the later part of the Cambrian period the enormous thickness of the Quebec group of North America appears to represent a broad stripe of deep water parallel to the eastern edge of the American plateau, and in which an immense thickness of beds of sand and mud was deposited with very few fossils, except in particular beds, and these of a more primordial aspect then those of the plateau itself. These rocks no doubt represent the margin of a deep Atlantic area, over which cold currents destructive of life were constantly passing, and in which great quantities of sand and mud, swept from the icy regions of the North, were continually being laid. The researches of Dr. Carpenter and Dr. Wyville Thomson show us that there are at present cold areas in the deeper parts of the Atlantic, on the European side, as we have long known that they exist at less depths on the American side; and these same researches, with the soundings on the American banks, show that sand and gravel may be deposited not merely on shallows, but in the depths of the ocean, provided that these depths are pervaded by cold and heavy currents capable of eroding the bottom, and of moving coarse material. The Quebec group in Canada and the United States, and the metalliferous Lower Silurian rocks of Nova Scotia and Newfoundland, destitute of great marine limestones and coral reefs, evidently represent deep and cold-water areas on the border of the Atlantic plateau. At a later period, the beginning of the Upper Silurian, the richly fossiliferous and exceptional deposits of the Island of Anticosti, formed in the deep hollow of the Gulf of St. Laurence, show that when the plateau had become shallowed up by deposition and elevation, and converted into desolate sand-banks, the area of abundant life was transferred to the still deep Atlantic basin and its bordering bays, in which the forms of Lower Silurian life continued to exist until they were mixed up with those of the Upper Silurian.