MOOE, STUDY OF THE MORRISON FORMATION 165 



With conditions such as those ahove outlined kept in mind as a work- 

 ing h3'pothesis, it is desirahle to consider the characteristic^ of large 

 alluvial fans and river flood-plains of recent and Pleistocene origin. 



Characteristics of Eecent Alluvial Plains 



Davis (1898, 6) describes the fan of the Hoangho Eiver in China as 

 follows : "One of the largest alluvial fans in the world is that of the 

 Hoangho, in eastern China. This great river, bearing a heavy load of 

 fine silt from the basins among the inner mountains, issues from its 

 inclosed valley 300 miles inland from the present shore-line, and at a 

 height of about 400 feet above sea-level, and then flows to the sea down 

 the gentle slope of its extensive fan." The fan is fertile and is subject 

 to overflow on a vast scale. A single flood in 1887 covered 50,000 square 

 miles and drowned at least 1,000,000 people. The course of the river 

 and its tributaries is constantly shifting. 



The fan of the Yangtse-Kiang lies immediately south of that of the 

 Hoangho and is more or less connected with it. The large rivers leave 

 the mountains in valleys which reseml^le estuaries in their form and rela- 

 tion to the mountains. T^he mountains may be compared to the land and 

 the plains and valley to the sea and estuary. The great rivers are bor- 

 dered on either side by lakes, swamps and other streams, which often 

 connect with each other in an intricate manner. The lakes vary in size 

 from small ponds to large lakes 50 miles or so in length. They are 

 usually situated in tracts along the borders of the large rivers, but are 

 sometimes situated far from the latter. They extend from the mountains 

 to the delta and are not especially characteristic of any one region. These 

 features are well shown on the German government's land sur\cy maps of 

 eestern China (1903, 9, 10; 1904, 9, 10, 11). 



Grabau (1914, 6) describes the dry delta of Cooper Creek as extending 

 over an area of 185 x 170 miles. Grabau describes the great alluvial 

 plain of the Indo-Gangetic region as follows : 



"The Indo-Gangetic alluvial plain is an example of a river plain 

 formed of many confluent dry deltas and carried forward by the two 

 great rivers of northern India — the Indus on the west and the Ganges, 

 with the tributary Brahmaputra, on the east. ISTunierous small streams 

 feed these rivers from the south slope of the Himalayas, carrying an 

 abundance of coarse and fine debris. . . . The great alluvial plain 

 extends over an area of about 300,000 square miles, and comprises the 

 richest and most populous portion of India. It varies in width from 90 

 to nearly 300 miles, and entirely separates the lower peninsula of India 



