138 PHYSICAL GEOLOGY 



its greatest extent covered 19,750 square miles and was 1000 feet 

 deep. At this time it had an outlet to the north which carried the 

 excess waters to the Pacific. During this period, too, great terraces 

 were cut and immense deltas were built. From Salt Lake City one 

 can see these terraces on the lower slopes of the mountains and from 

 them can learn the former levels of the lake. A change in climate 

 finally reduced this extensive lake to the present relatively small 

 Great Salt Lake, which has an area of 2000 square miles and an 

 average depth of 15 feet. Since the water now contains 18 per cent, 

 of salt, it is so dense that the bather is required to exert no effort to 

 keep his head above water, as it is impossible to sink. 



REFERENCES FOR THE WORK OF STREAMS 



General 

 Cleland, H. F., — North American Natural Bridges, with a Discussion of their 



Origins: Bull. Geol. Soc. America, Vol. 21, 1910, pp. 313-338. 

 De Martonne, E., — Geographie Physique, pp. 413-442. 

 Gilbert, G. K., — Report on the Geology of the Henry Mountains : U. S. Geog. and 



Geol. Surv. of the Rocky Mountain Region, 1877, pp. 99-150. 

 Haug, E., — Traite de Geologie, pp. 406-436. 

 Russell, I. C, — Rivers of North America. 

 Salisbury, R. D., — Physiography {Advanced), pp. 114-203. 

 Salisbury and Atwood, — The Interpretation of Topographic Maps: Professional 



Paper, U. S. Geol. Surv. No. 60, 1908. 

 Shaler, N. S., — Aspects of the Earth, pp. 143-196. 

 Taylor, F. B., —Niagara Falls Folio : U. S. Geol. Surv. No. 190, 1913. 



Flood Plains 

 Davis, W. M., — The Development of River Meanders: Geol. Mag., Vol. 10, 1903, 



pp. 145-148. 

 Jefferson, M. S. W., — Limiting Widths of Meander Belts : Nat. Geog. Mag., Vol. 13, 



1902, pp. 373-384. 



Cycle of Erosion 

 Davis, W. M., — Geographical Cycle, Geographical Essays, 1909. 

 Davis, W. M., — Base Level, Grade, and Peneplain: Jour. Geol., Vol. 10,1902, 



pp. 77-109. 

 Davis, W. M., — The Peneplain: Am. Geologist, Vol. 23, 1899, pp. 207-239. 



Stream Piracy 



BOWMAN, I., — A Typical Case of Stream Capture in Michigan: Jour. Geol., 



Vol. 12, 1904, pp. 326-334. 

 Dak ion, \. H., — Examples of Stream Robbing in the Catskill Mountains: Bull. Geol. 



Soc. America, Vol. 7, 1896, pp. 505-507. 

 . W. M., — Stream Contest along the Blue Ridge: Bull. Geog. Soc. Philadel- 



plii.i, Vol. 3, 1905, pp. 213-244. 



