=The shelf ice of the ice age.=—Shelf ice, such as we have become familiar with in Antarctica as a marginal snow-ice terrace floating upon the sea, no doubt existed during the ice age above the Gulf of Maine (see Fig. 324, p. 298), and perhaps also over the deep sea to the westward of Scotland. Though the inland ice probably covered the North Sea, and upon the American side of the Atlantic the Long Island Sound, both these basins are so shallow that the ice must have rested upon the bottom, for neither is of sufficient depth to entirely submerge one of the higher European cathedrals. [Illustration: FIG. 344.—Outline map of the front of the Green Bay lobe of the latest continental glacier of the United States. Drumlins in solid black, moraines with diagonal hachure, outwash plains and the till plain or ground moraine in white (after Alden).] =Character profiles.=—All surface features referable to continental glaciers, whether carved in rock or molded from loose materials, present gently flowing outlines which are convex upward (Fig. 345). The only definite features carved from rock are the _roches moutonnées_, with their flattened shoulders, while the hillocks upon moraines and kames, and the drumlins as well, approximate to the same profile. The esker in its cross sections is much the same, though its serpentine extension may offer some variety of curvature when viewed from higher levels. [Illustration: FIG. 345.—Character profiles referable to continental glacier.] READING REFERENCES FOR CHAPTER XXII General:— JAMES GEIKIE. The Great Ice Age. 3d ed. London, 1894, pp. 850, maps 18. CHAMBERLIN and SALISBURY. Geology, vol. 3, 1906, pp. 327-516. FRANK LEVERETT. The Illinois Glacial Lobe, Mon. 38, U. S. Geol. Surv., 1899, pp. 817, pls. 34; Glacial formations and Drainage Features of the Erie and Ohio Basins, Mon. 41, _ibid._, 1902, pp. 802, pls. 25; Comparison of North American and European Glacial Deposits, Zeit. f. Gletscherk., vol. 4, 1910, pp. 241-315, pls. 1-5. Former glaciations previous to Ice Age:— A. STRAHAN. The Glacial Phenomena of Paleozoic Age in the Varanger Fjord, Quart. Jour. Geol. Soc., London, vol. 53, 1897, pp. 137-146, pls. 8-10. BAILEY WILLIS and ELIOT BLACKWELDER. Research in China, Pub. 54, Carnegie Inst. Washington, vol. 1, 1907, pp. 267-269, pls. 37-38. A. P. COLEMAN. A Lower Huronian Ice Age, Am. Jour. Sci. (4), vol. 23, 1907, pp. 187-192. W. M. DAVIS. Observations in South Africa, Bull. Geol. Soc. Am., vol. 17, 1906, pp. 377-450, pls. 47-54. DAVID WHITE. Permo-Carboniferous Climatic Changes in South America, Jour. Geol., vol. 15, 1907, pp. 615-633. Driftless and drift areas:— T. C. CHAMBERLIN and R. D. SALISBURY. Preliminary Paper on the Driftless Areas of the Upper Mississippi Valley, 6th Ann. Rept. U. S. Geol. Surv., 1885, pp. 199-322, pls. 23-29. R. D. SALISBURY. The Drift, its Characteristics and Relationships, Jour. Geol., vol. 2, 1894, pp. 708-724, 837-851.