108 



The scarcity of algte can best he explained by cousideiing the nature 

 of the river itself. Along the lower part of the West Fork and the entire 

 course after the two branches unite the river follows a meandering course 

 through a loose, sandy soil; and, by a gradual process of cutting the bank 

 on one side and piling up sandbars on the other, it is continually clianging 

 its course. Then, along the straight parts of the stream the banks are 

 generally steep, and there is little shallow water. When we consider at 

 the same time that the current is comparatively swift, it is seen that only 

 when the river is at its lowest stage are conditions at all fa\-orable for the 

 growth of alga\ Moreover, the conditions just preceding these investiga- 

 tions had been the worst possible, for the exceptional flood of the preceding 

 spring had made such changes in the ri\er bed that several yenrs will be 

 required to bring the plant life of the stream back to a normal condition. 



The abrupt disaiipea ranee of algal growth just below Martinsville was 

 accomi)anied by an improved sanitary condition of the water. These two 

 conditions were due. in part, to a series of long, deep stretches of (luiet 

 water which acted as septic basins for the polluted water and were also 

 loo deep for algx. It is probable, too, that the alg;e above these deep parts 

 aided materially in purifying the water by releasing large amounts of 

 (ix.\gcn which went into solution and hastened the putrefaction of organic 

 matter. 



