436 STUDIES FOR STUDENTS 



Indus Delia: 



C. W. Trememheere, Journal of the Geographical Society, Vol. XXXVII 

 (1867), pp. 76, 81, and plate. 



Ganges Delta: 



James Fergusson, Quarterly Journal 0} the Geological Society, Vol. XIX 

 (1863), plate, pp. 352, 353. 



Basin 0} Minas: 



Charles Lyell, Travels in North America, Vol. II (1855), p. 166. 



N. S. Shaler, "Sea Coast Swamps of Eastern United States," Sixth Annual 



Report (1885), United States Geological Survey, p. 368. 

 J. A. Bancroft, "Ice-Borne Sediments in Minas Basin," Proceedings and 



Transactions, Nova Scotian Institute of Science, Vol. XI (1905), Part 



I, p. 161. 



From the preceding facts a number of principles governing the 

 development of the littoral zone may be drawn. 



With lunar tides of less than 2 . 5 feet storm tides become of greater 

 importance. The development of extensive mud-flats and salt 

 marshes takes place in protected places. In exposed places the 

 cutting action of the waves prevents either from forming. Mud-flats 

 exposed at low tide become conspicuous with tides of about 6 feet 

 range. When the tide is 10 feet, these may form belts a mile wide, but 

 broken up by tidal channels. With higher tides there is but little ten- 

 dency to increase the width of exposed flats, but the material consti- 

 tuting them may become coarser, the Gallegos River in Patagonia, 

 where the tides reach 46 feet, showing lower flats composed of gravels 

 and even of coarse bowlders. ^ With the larger tides the tidal chan- 

 nels for draining the tidal marshes are wide and deep, forming con- 

 venient protected passages for the larger vessels through silted-up 

 estuaries or behind the barrier beaches. 



The salt marshes are built up to near the upper limit of tidal 

 flooding. Where storm tides are the most important the system of 

 drainage of these marshes is very imperfect. With tidal range of 

 from 4 to 6 feet this becomes developed, and with a range of from 

 10 to 16 feet they become rivers in size, capable of quickly leading 

 an immense volume of water into the limits of the tidal area, but 

 more important for quickly draining the tidal grounds during the 

 ebb. The width of the salt marshes appears to be less dependent 



I J. B. Hatcher, Princeton Patagonian Expeditions, Vol. I, Fig. 33, and p. 239. 



