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.
R. H. Whitbeck. Contrasts between the Glaciated and the Driftless Portions of Wisconsin, Bull. Geogr. Soc., Philadelphia, vol. 9, 1911, pp. 114-123.
Glacier gravings:—
T. C. Chamberlin. The Rock Scorings of the Great Ice Invasions, 7th Ann. Rept. U. S. Geol. Surv., 1888, pp. 147-248, pl. 8.
The dispersion of the drift:—
R. D. Salisbury. Notes on the Dispersion of Drift Copper, Trans. Wis. Acad. Sci., etc., vol. 6, 1886, pp. 42-50, pl.