THE INFLUENCE OF FLOODS UPON ANIMALS 165 



cans Le Sueur, red-horse Maxostoma sp. (?), and bullheads 

 Ameiurus natalis Le Sueur, several weeks and even months af- 

 ter the recession of the flood. Coker (1915) calls attention to 

 the fact that the number of fish Ls diminished by young fish be- 

 ing earner awa}" from the stream during overflow. 



The cutting of new channels is to be considered under the 

 sculpturing of the flood-plain at least until such are claimed by 

 the stream when in its normal condition. The cutting of one 

 such channel is indicated on the map, figure 16. Figures 25 and 

 26 show scenes viewed from the bottom of the cut. 



The deposition of material upon the flood-plain is almost in- 

 variably the direct result of the washouts just mentioned. The 

 soil materials scooped out to form these holes in the flooded 

 plain are capable of being carried in inverse proportion to their 

 coarseness, the gravel and sand usually being deposited imme- 

 diately below the washout while the soil proper, loam, clay, etc., 

 is often carried in suspension by the w^ater for a much longer 

 distance. This has its most important effect upon animal life 

 indirectly through its alterations made in the character of the 

 vegetation. All animal life, we know, depends either directly 

 or indirectly upon plant life, and many animals are limited to a 

 small number of plant species for food. Even certain of the 

 predaceous animals are limited to a relatively small number of 

 animal species for prey and the parasitic forms naturally depend 

 upon one particular host. The flood-plain is especially rich in 

 mesophytic plants with a corresponding wealth of animal spe- 

 cies. In the case of cultivated flelds the animal life is more or 

 less distinct, depending upon the nature of the plants under 

 cultivation. The materials deposited by the floods may be 

 roughly classified in this relation as (1) sterile, i. e., sand and 

 gravel, and (2) fertile, i. e., silt. Grravel bars built up in the 

 midst of the fertile flood-plain (figures 27 and 28) are in some 

 ■cases for years practically barren of both plant and animal life. 

 A deposition of silt may have either of two effects. It may be 

 laid upon a stretch of gravel rendering, in the course of a few 

 months, an area, sterile and waste, into a tangle of grasses and 

 herbaceous plants with most complex animal associations being 

 developed and maintained. On the other hand, cultivated fields, 

 blue grass pasture lands or waste places in which a great wealth 

 of native plants have ])ecome established may receive this layer 

 of silt and the area will be obliged to undergo a complete sue- 



