110 PHYSICAL GEOGEAPHY. 



Dakota and Nebraska, and of its western limits in the 

 latter State and Kansas. It is known, liowever, to extend as 

 far west as the valley of the Elkhorn in Washington county, 

 Nebraska, some twenty -five or thirty miles west of the 

 Missouri river. There is reason to "believe also that it 

 occnpies a continuous region of an equal average width, 

 bordering that great river, and extending as far south as 

 Kansas river. In Missouri, it occupies a large area adjoining 

 that of Iowa, the whole having been, originally, an united and 

 continuous deposit before the Missouri river had eroded its 

 valley out of and through it. What its southern limits are 

 is not known, but it is reported by Prof. Swallow, of Missouri, 

 to extend far down into that State. 



The Bluff Deposit is thus known to occupy a region through 

 which the Missouri river runs almost centrally, and measures 

 as far as is now known, more than two hundred miles in 

 length and nearly a hundred miles wide. 



The thickest part of the deposit yet known is in Fremont 

 county, where it reaches a thickness of at least two hundred 

 feet above the drift. There is reason to believe that its 

 thickest part is in the immediate vicinity of the valley of the 

 great river, because it occupies almost equal areas on each 

 side, and thins out in all directions from it to the outer 

 margins of the deposit. The whole height of the bluffs in 

 Fremont county, is at one or more points about thiee^ 

 hundred feet above the flood-plain of the Missouri river; but 

 in that case one hundred feet of it is made up of the Upper 

 coal-measure strata and drift which supports the Bluff 

 Deposit. Going northward from that county along the line 

 of the bluffs, the Upper coal-measure strata are seen for the 

 last time, in that direction, at their base a few miles north of 

 Council Bluffs. The next stratified rocks to be found by con- 

 tinuing northward, are of Cretaceous age. These are found 

 occupying the base of the bluffs in Woodbury county, first 

 appearing at the town of Woodbury, seven miles below Sioux 

 City. The distance between the most southerly point in the 

 line of bluffs at which the Cretaceous strata are exposed, and 



