1090,091] DENUDATION OF " SILT " AND " LOAM " 819 



690. As for the calcareous silt, (No. '-'37), the analysis shows it to possess an 

 adequate supply of all the elements of a good soil ; its peculiarity being the 

 high percentage of the Carbonates of Lime and Magnesia which it contains, and 

 a remarkable deficiency in Alumina. Its admixture of clay is so slight as to 

 barely entitle it to the name of Loam, its main body being silex, in a state of 

 fine division, with but a few per cent, of coarser sand. Hence the small amount 

 of moisture which it is capable of absorbing, in view of which it is somewhat 

 surprising that it should not be a remarkably drouthy soil. This is perhaps 

 owing to its large dose of lime, the property of preventing injury from drouth 

 being particularly claimed for that substance. 



It seems, nevertheless, that injury from drouth is more frequently sustained 

 on soils formed by this silt alone, than on those derived from the brown loam ; 

 owing probably to the absence of a more retentive subsoil, in the former case. 

 For it must be recollected, that while the lightest soils overlying the brown 

 loam are sure to have a clay foundation at no great depth, no such change ever 

 occurs where the calcareous silt forms the soil. Vertical wells of 50 feet of the 

 latter, will most generally show such a conformity of material, that specimens 

 taken from the remotest portions of the mass, cannot frequently be distinguished 

 from one another. When a drouth ensues after a heavy rain on well worked 

 soils of the silt character, these frequently crack open to the same extent as the 

 heavy soils of the prairies and Flatwoods (n402 1 t to 404), causing great injury 

 to the crops. 



69 1 . The analyses above given represent, probably, the extremes 

 of both kinds of soil, such as they are frequently found on the 

 level uplands and hilltops, and the silt soil on the upper portion 

 of the hillsides. The lower portion (talus) of the latter, however, 

 is commonly a mixture of the two, in variable proportions — a 

 necessary consequence of their mode of formation, having been 

 washed down from above. It is observable, however, that in the 

 great majority of cases (and especially where the brown loam now 

 occupies the summit level) the soils and subsoils of the talus differ 

 but little in their appearance as well as in their agricultural 

 properties, from those of the hilltops ; though as a general thing, 

 they are said to produce, rather more freely, and to last longer. 



The relations between these several soils will be better understood by 

 reference to the diagram (No. 6), which illustrates the progress, and different 

 stages of denudation ; the space ruled vertically representing the brown loam 

 stratum ; that ruled liorizontally, the calcareous silt ; and the oblique ruling, the 

 talus, consisting of a mixture of the two, as washed down the hillside and 

 appearing at the foot. In No. 1, of this diagram, we have a broad ridge or 

 table-land, evenly covered with the brown loam, whereas the calcareous silt 

 appears only on the upper portion of the hillside, and the talus is comparatively 

 inconsiderable as yet. — In No. 2, denudation has progressed so far as to remove 

 the greater portion of the loam stratum from the summit of the ridge, it being 

 left only in depressions, and quite shallow ; so that in places, the calcareous 

 silt appears on the surface ; the talus, at the same time, being of greater extent 

 than before. — In No. 3, the removal of the brown loam from the summit of the 

 ridge has been completed ; it has all been washed down the hillside, intermin- 

 gled with the silt, and the latter now imparts its peculiar character to the ridge, 

 which has steep slopes and a sharp summit ; as is the case in the ridges between 

 Port Gibson and Grand Gulf. 



