584 PRINCIPLES OF STRATIGRAPHY 



may be mentioned that of the Merced in California, of the Garonne 

 at the northern base of the Pyrenees, the delta of the Cooper River 

 in the Lake district of South Australia, the great tiood plain delta 

 of the Huang-ho or Yellow River of China, and the similar but 

 compound Indo-Gangetic delta plain of northern India. 



The Merced River of California rises in the Sierra Nevadas and 

 carries much waste down their steep western slopes. Reaching the 

 broad open valley of California, which lies between the Sierra and 

 the Coast range, it has built a fan which at present has a radius 

 of about 40 miles. This consists of gravel near the mountain, and 

 of fine silt at a distance. On account of the gentle slope of the 

 surface, the water is turned readily from one channel into the other 

 at the head of the fan. 



"The many rivers issuing from the valleys of the Sierra Ne- 

 vada and the Coast range upon the 'Valley of California' have 

 formed an extensive plain, of which the Merced fan, ... is 

 only a part. The successive fans are so broad and flat that their 

 slightly convex form can hardly be recognized without the aid of 

 surveying instruments. j\Tearly all the streams run in shallow chan- 

 nels, but little beneath the gently sloping surface of the fans. The 

 fans from the east and west meet in a broad, flat-floored trough." 

 (Davis-iSii-pj.) 



River-made plains of this type are formed on both sides of the 

 Alps. Those on the south have begun to cut valleys into the old 

 deposits, while those on the north have cut to a depth of 1,000 feet, 

 leaving the former plain as a series of ridges. The river Po flows 

 eastward between the broad plain built by the rivers from the high 

 Alps on the north, and the narrower one built by the streams from 

 the lower Apennines. Where it enters the Adriatic Sea the Po 

 builds a normal delta. 



While the material of this river plain is typically a subaerial 

 deposit, intercalated marine beds are not wanting. They have been 

 reported from the Venetian region where they represent periodic 

 encroachment of the sea. (Penck-41.) 



One of the most extensive of modern dry deltas is that of 

 Cooper Creek in the Lake district of South Australia. Its area is 

 more than twice that of the Nile delta, its length being nearly 185 

 miles and its width over 170 miles. The water in the river, how- 

 ever, is abundant only after strong rains, the various distributaries 

 being changeable canals on the surface of the delta. (Peter- 

 mann-43.) 



Even larger than the Cooper Creek alluvial fan is that of the 

 Huang-ho or Yellow River of Ching. Its head is about 300 miles 



