[68] Figs. 165–168 are based on reports of Hayes, and Hayes and Campbell, already referred to. Drawn by E. S. Bastin.
[69] A question might be raised in this case as to what should be called the source. A spring issues from beneath the surface and flows away in a stream. The stream is said to begin where the water appears at the surface, though in some cases the water of the spring was a subsurface stream before it reached the surface. Water escaping from beneath a glacier as a stream may likewise be considered a spring at the point of its issue.
[70] Davis. Science, Vol. X, p. 142, 1887.
[71] L. C. Johnson. Bull. Geol. Soc. Am., Vol. II, pp. 20–25, 1891.
[72] Jefferson. Nat’l Geog. Mag., Vol. XIII, pp. 373–84.
[73] According to map published by the Mississippi River Commission in 1887.
[74] Russell. Rivers of North America, p. 114.
[75] Gilbert. Am. Jour. Sci., Vol. XXVII, 1884, pp. 427–34.
[76] Cooley. Rept. U. S. Engineers for 1879–80, Pt. II, pp. 1060 and 1071.
[77] Gerber. Cited by Todd. Bull. 158, U. S. Geol. Surv., pp. 150, 151.