FORMATION OF VALLEY BLUFFS. 21 



The valley bluffs of all the prairie streams seem to have 

 been the original banks of ri vers once entirely occupying 

 what is now valley, and doubtless then extending in depth 

 to where the permanent formation of which the bluffs are 

 composed now underlie both streams and valleys ; and 

 which, filling up gradually in the lapse of ages to their 

 present level by deposit of the sand washed down and 

 carried in suspension by the waters from the upper country, 

 have become the bottoms through which the present streams 

 remnants of those mighty rivers now wind their devious 

 courses. To this, as to all theories, there is a stumbling- 

 block ; there are localities where the valleys of these rivers 

 temporarily lose their continuity by there being a bluff on 

 only one side of them ; on the other, the rise to the general 

 level of the country being so gradual as not to be perceptible 

 to the eye. These expanses -would therefore have been 

 immense river back-waters ; places where drift of all kinds 

 would accumulate, and an aquatic vegetation flourish ; 

 possibly some of the coal-fields were once such. 



An old and well-worn buffalo trail of about twenty feet 

 in width, beaten hard by many a year's annual migration, 

 gave us easy access up the face of the bluff to the level 

 ground above ; and, on attaining it, we took the course we 

 judged would bring us to the valley again in ten or fifteen 

 miles. Our direction and conjecture as to distance proved 

 correct, and after about twelve miles' travelling we again 

 arrived at the edge of the general level, but at a place where 

 descent was impossible, the bluff being there perpendicular, 

 and over two hundred feet in height. 



The river was flowing below us, now hiding behind the 



