ADAMS COUNTY. 45 



by the annual floods of the river. In the vicinity of the bluffs, these deposits 

 are annually increased by the wash from the adjacent hills, and the sediments 

 that are carried down by the small streams during their frequent overflows. 



The valley of the Mississippi has been excavated in solid limestone strata, 

 to the depth of from one hundred and fifty to three hundred feet or more, and 

 from five to ten miles in width, and as we frequently find some portions of 

 this valley still occupied by beds of unaltered drift material, exactly like that 

 which covers the adjacent highlands, we have undoubted evidence that it was 

 not formed by the river which now, in part, occupies it, but is due to some 

 other and more potent agency, dating back to a period long anterior to the for- 

 mation of the existing water courses. It is very evident, that the surface of 

 the stratified rocks in this portion of the State, have been subjected to the 

 action of powerful denuding forces, anterior to the accumulation of the super- 

 ficial materials which now occupies the surface, by which these rocks were 

 greatly eroded, and in many places cut into deep valleys, some of which now 

 form our river courses, while others are wholly or partially filled with Drift 

 and Post Tertiary beds, and it is highly probable that, if we could see a com- 

 plete section of the beds which now occupy these ancient valleys, we should 

 find beneath the alluvial beds already described, deposits even older than any 

 which now cover the adjacent highlands. Along the banks of the water 

 courses, we find only from ten to twenty feet of the alluvial beds exposed by 

 natural causes, and the character of the underlying strata can only be deter- 

 mined by artificial excavations. 



The next older division of this system, is the Loess, a deposit of marly sand 

 and clay, which ranges in thickness from ten to forty feet, and attains its greatest 

 development where it caps the river bluff's, thinning out rapidly towards the 

 adjacent highlands, which form the summit level of the interior portion of the 

 county. It is usually of a light buff, brown, or ashen gray color, frequently 

 showing distinct lines of stratification, and always overlies the drift clays, 

 when both are present in the same section. It is usually quite sandy, where 

 it caps the river bluffs, but becomes more argillaceous at other points where 

 the beds are thinner, and, locally, it becomes quite calcareous. The Loess is 

 well exposed in the bluffs at Quincy, where it is about forty feet in thickness, 

 and overlies some beds of plastic clay and sand, which are probably of Post 

 Tertiary age, and older than the true drift. Immediately above the limestone 

 here, we find a few feet in thickness of what might be called " local drift," 

 consisting of angular fragments of chert, embedded in a brown clay, which 

 have probably been derived from the subordinate limestones. This is overlaid 

 by a few feet of blue plastic clay and stratified sands, on which the Loess is 

 deposited. At one point, near the base of the bluffs, in the northern part of 

 the city, we observed underlying the Loess, what seemed to be a chocolate 



