VALLEY FILLING BY INTERMITTENT STREAMS 221 



Evidently that seventy-five- or eighty-year-old tree started as a 

 sapling in the valley bottom when the surface was two and one- 

 half feet below the present surface and on a level with the upper 

 portion of dark soil. Filling must have taken place some time 

 within the seventy-five or eighty years. It is probable that filling 

 has extended over many years and was and is necessarily inter- 

 mittent during the year and intermittent during periods of years, 

 less waste being furnished when the field to the west is in sod and 

 during the dry periods of the year. 



If all these suppositions be true, one would be led to make the 

 statement that all valleys of intermittent streams that head in culti- 

 vated fields are waste filled. To test this generalization search was 

 accordingly made and within a quarter of a mile from Jewell's 

 Creek three others were found that showed essentially the same 

 features as here described. Later, other valleys were examined, 

 in all about a dozen, and invariably it was found that where these 

 streams headed in cultivated fields filling was going on in the 

 valley, the amount of filling depending upon the size of the collect- 

 ing area and upon the kind of material. Not all showed steps as 

 we have in Jewell's valley, but in most of the valleys this feature 

 was duplicated. It was found that the steps were probably pro- 

 duced by bowlders or brush accumulating in the valley, causing a 

 deposit of leaves and waste on the up-side. 



The steps in Jewell's Creek as a rule are higher than any in the 

 other valleys yet examined. The ones that are higher show evi- 

 dences of their being in rapid though intermittent recession, and 

 from indications on the sides of the valley it is believed that they 

 started farther down the valley where stones and twigs blocked 

 the course of the stream. How could the higher steps be produced 

 then ? Let us imagine that we have a gradual slope to the valley 

 floor above this point of blocking, and that at some points the 

 water in times of flood had broken through the grassy cover of the 

 slope and had gouged out a trough with a tiny cliff at the upper 

 portion, as we see just to the north of the walnut tree in both 

 picture and map. Now by recession of this tiny step the cliff at 

 the edge would become higher and higher because the new valley 

 bottom produced by erosion would have less grade than the pre- 



