257 
the chief problem. Why do not deltas occur on all of the hundreds of 
streams that score the valley sides? Why did one stream a mile or two 
long build a delta a few rods in area while a much longer stream near by 
Fig. 2. Briggs Delta. A. From below. B. From above. 
built none? The answer seems to be that such features have no prolonged 
history, but owe their existence to a single local and brief accident of 
drainage which did not affect neighboring streams, 
[1723003] 
