198 GEOLOGICAL REPORT. T334, 335, 336 



of the deposition of this loam, the larger channels were already more or less im- 

 pressed upon the surface, and high ridges existed which remained above the level 

 of the water which deposited the loam : the minor denudations which have 

 caused the present undulating surface, had as yet exerted but little influence. 

 The lines of contact between the Orange Sand and loam, where the latter is 

 decidedly in situ, are generally much less undulating, than are those between the 

 Orange Sand and the older formations. 



334. Under the present configuration of the surface, however, we find precisely 

 the same stratigraphical relations to exist between the Orange Sand and 

 the loam stratum, as those which we see between the latter and the calca- 

 reous silt of the Bluff formation, as exemplified in Diagram No. 6 (see "Southern 

 Eiver Counties") ; that is to say, the loam has to a great extent been removed 

 from the level hilltops or plateaux where it was originally deposited, to the 

 hillsides and valleys, leaving the higher portions of the ridges more thinly 

 covered or altogether bare. The same agencies which are at work at present, 

 carrying away the arable soils from our uplands, will explain the hillside posi- 

 tion in which, in the more hilly uplands of Mississippi, this loam is prevalently 

 found at the present time ; while, whenever extensive level or slightly undula- 

 ting tracfs exist, it may be seen to rest conformably upon the Orange Sand 

 strata. 



335. Its prevalent character in what I have termed the Yellow Loam Region 

 of the State, is that of a mellow clay or loam, without any definite structure 

 or cleavage, variously tinged with iron ; containing from 10 to 25 per cent., 

 usually, of siliceous sand, the rest being clay mixed with finely divided silex, 

 and forming, therefore, rather loose, mellow soils, and good brick-clays. It almost 

 invariably contains some irregular whitish veins of sand, especially in its lower 

 portions, where it overlies the Orange Sand ; and sometimes, but not most 

 frequently, passes into the materials of the latter by degrees of transition, 

 through a sandy "hardpan," which in some localities attains a considerable 

 thickness (10 to 15 feet) and may correspond to the "altered drift" of Prof. 

 Swallow (Report of the Geological Survey of Missouri, p. 76). Where, how- 

 ever, the loam overlies clayey strata, it becomes heavier as we proceed down- 

 wards ; and if they be rich in lime, this ingredient is also found in increased 

 quantity in its lower layers. In the latter case, the fair yellow or brown color of 

 the loam almost invariably acquires a greenish hue, even where full exposure to 

 the atmosphere places a reduction of the peroxide to the protoxide out of 

 question. Such is very generally the case in the prairie regions of the State, 

 whose loam stratum (overlying the Rotten Limestone in the cretaceous, and 

 sometimes the clay marls of the tertiary region). I believe to be essentially 

 contemporaneous with that of the hills, since, so far as comparable, its geological 

 characters are very similar. 



336. That forming the surface stratum in the "Northeastern Prairie Region," 

 is certainly not cretaceous (as has been, with some doubt, suggested by Tuomey) ; 

 for it contains none of the fossils of that formation, except where it is in 

 immediate contact with the rock ; and no proper fossils whatsoever, (except in 

 the alluvium immediately bordering on the streams*) ; while on the edge of the 

 prairies, the greenish-yellow underclay of the prairie soil is often distinctly seen 

 overlying the Orange Sand, and passing insensibly into the common loam. It 

 is but very indistinctly stratified, and very nearly the same in appearance, from 

 the top to the bottom of the stratum, which is sometimes 10 to 15 feet in 

 thickness (on the prairies of Monroe), viz : a heavy, massy clay, containing but 

 little sand (and that coarse), and a large number of smooth, hard, round 

 concretions of Brown Iron Ore, from the size of sand-grains to that of buckshot, 



*The "prairie fossils" mentioned in L. Harper's Report (p. 109, ff.) were, to 

 my personal knowledge, collected in the neighborhood of streams in the prairie 

 region. 



