100 



PHYSIOGRAPHY 



River of Louisiana long ago. It appears to have been in reality a 

 tree jam. The trees appear to have fallen into the river by the 



undercutting of forested banks by the 

 meandering stream. Floating down 

 with their branches, the trees lodged 

 against the banks. The lodging of 

 some trees caused others to be 

 stopped, and so the jam, or raft, grew. 

 By obstructing tributary valleys, the 

 raft ponded their waters, and so gave 

 rise to lakes (Fig. 107). The raft 

 was cleared away in 1867, and since 

 that time many of the former lakes 

 have been drained and some of their 

 former bottoms are now cultivated. 

 In deltas, deposits are sometimes 

 so distributed as to enclose bodies 

 of water (Fig. 99) which become 

 lakes. The alluvial cones or fans 

 built by tributary valleys become so 

 large, in some cases, as to obstruct a 

 mountain valley, giving rise to a pond 

 or lake above. The basin of Lake 



BORMAT PWUMM CO., N.V. 



Fig. 107. Lakes along the Red 

 River of Louisiana. The lakes 

 are at the lower ends of the 

 tributary streams. 



Tulare in California was formed in this way. 



REFERENCES. 



1. RUSSELL, Rivers of North America: Putnam, 1898. 



2. WALCOTT, Natural Bridge of Virginia: Nat. Geog. Mag., Vol. V, 1893, 

 pp. 59-62. 



3. JOHNSON (L. C.), The Nita Crevasse: Bull. Geol. Soc. of Am., Vol. II, 

 pp. 20-25, 1891. 



4. GANNETT, The Flood of April, 1897, in the Lower Mississippi: Scot. 

 Geog. Mag., Vol. XIII, 1897, p. 419. 



5. WILLIS, The, Northern Appalachians, in Physiography of the United 

 States: Am Bk. Co., 1896. 



6. HAYES, The Southern Appalachians, in Physiography of the United 

 States: Am. Bk. Co., 1896. 



7. SALISBURY, Physiography, Advanced Course, Chapter IV: Henry Holt&Co. 



8. Standard text-books on Geology. 



