328 ISAIAH BOWMAN 



When the encroachment of the bend of the Huron River began, 

 Oak Ravine constituted the upper part, and Oak Run the lower part 

 of a single valley, discharging into Willow Run; but when the right 

 bank of their common valley had been broken down by the attack of 

 the Huron, the waters of the headward portion were diverted and 

 cascaded down the bluff of the embayment to the Huron below, while 



Fig. 2. — Oak Run Valley where headwaters are taken out to left. 



the part of the channel seen in the foreground of Fig. 2 was left a 

 marshy fiat. At the present time these two valleys, once continuous, 

 have a difference of elevation- of thirty feet, due to the erosion of the 

 bottom of the upper section, while the head of the lower section has 

 not been appreciably lowered. 



The drainage area of the lower section, now the valley of Oak 

 Run, is very small, probably less than 100 acres. The drainage 

 area of the diverted upper section is several hundred acres. The 

 difference in the erosion since the disseverance of the valley has 

 brought the configuration of the two portions into sharp contrast. 

 That of the lower portion at its head, where erosion has practically 



