Surber. — Biological Surveys in Minnesota. 229 



from the uplands, and gathering momentum as it passes through 

 the deep ravines and gullies, greatly accelerating the action of 

 erosion; and while much of the silt, or soil, of the uplands is 

 carried onwards to the main valley of the Mississippi, vast quanti- 

 ties are deposited on the beds of the smaller streams, so that we 

 find once clean rocky beds are well covered by this sediment. 



The removal of the heavy sod formerly covering our prairie 

 lands, the deforestation of the hardwood forest belt, with the 

 attending removal of the centuries-old accumulation of humus and 

 the destruction by fire and pasturage of low-lying shrubbery among 

 the groves of forest left standing creates conditions having tre- 

 mendous influence on the water supply, in that such lands no 

 longer absorb and hold for gradual release the rainfall on which 

 our springs depend ; but, being underlaid with a subsoil or stratum 

 of earth impervious to water, the rainfall rushes off in torrents as 

 soon as it falls. This condition particularly applies to the south- 

 eastern counties where, as a result of the deforestation and suc- 

 ceeding intensive cultivation of the uplands, we find many springs 

 so reduced in flow as to have become entirely inadequate to sustain 

 even small running brooks during long continued hot weather, 

 when, of course, evaporation reaches its maximum. This is but 

 one step removed from actual stoppage of flow, and where such 

 conditions exist over an extensive territory, as it does in this in- 

 stance, it has so reduced the flow in the main streams for miles 

 below, that we can readily become reconciled to the fact that at 

 no long deferred future date such streams will have become inter- 

 miuent in character, and eventually run only immediately follow- 

 ing heavy precipitation. Much of this has been brought about by 

 the necessities of civilization. 



The lesson this teaches us is that the permanence of any stream 

 depends primarily on its fountain heads and these in turn are de- 

 pendent on the adaptability of the soil and its covering of humus 

 to absorb and hold moisture. There can be no sadder experience 

 for the practical conservationist than to wander along a stream 

 bed holding here and there a pool of stagnant water where once a 

 rushing flood full of life meandered its way, and to observe along 

 its course the conditions of wooded banks and slopes conducive to 

 far different results had its headwaters been protected by standing 

 forest or undrained marshes. 



