32 CLASSIFICATION OP SOILS. 



enough to be injurious, in any of the modes indicated to the phy- 

 sical properties above stated of that earth. No such soil exists in 

 all Virginia, nor in any other of the Atlantic States north of 

 Florida. 



As these general divisions of soils are determined according to 

 their predominating or most operative physical ingredient only, 

 the term calcareous soil (of which such frequent use will be made 

 in this essay) has been designedly omitted above. But to prevent 

 misapprehension, it will be merely mentioned, in anticipation, that 

 calcareous soil will be hereafter used as a still more comprehensive 

 term, embracing not only all the super-calcareous soils, but all 

 others that contain even the smallest appreciable proportion of car- 

 bonate of lime. Generally, however, the term calcareous will be 

 that applied to soils in reference to their contents of small and 

 harmless proportions of carbonate of lime (acting as a chemical 

 constituent only or mainly) ; while those having larger and hurtful 

 proportions will always be contra-distinguished as the chalky or 

 super-calcareous.* 



4. A magnesian soil would be one in which magnesian earth 

 is in sufficient excess to make its physical qualities predominate 

 over the other earths serving as ingredients. Such soils are of 

 doubtful existence ; certainly of extremely rare occurrence. 



5. A Jiumicy j>e,aty ', or vegetable soil, has so large a proportion 

 of humus that it is either injurious to production, or otherwise 

 serves to counteract and overbalance the opposite injurious qualities 

 of some other ingredient. Thus, a soil which by its aluminous 

 constitution alone would have been very clayey, or another which 

 would otherwise have been chalky, might have either of such de- 

 fects of texture, &c., counteracted, and partially remedied, by a 

 greater predominance of humus ; and thereby be made a humic 

 instead of either a clayey or chalky soil. 



For an earth to be predominant and excessive in a soil, as un- 

 derstood above, and so to convey its qualities and its name, it is 

 not necessary that it shall be the ingredient greatest in quantity 



* The previous difficulties of defii-lcion and of undc. V.pr ._ g on 

 head, woul 1 be greatly iner^ed bv a;>.'.;i'i:.g the strange r.::.:,.:r jlatur 

 the latest writer, Profess r J. ... ,:on, whose authority stands so 



Irigh, and is so generally vrovtLy of respect. He confines iao term "cal- 

 careous sou" (by express defin.tion) to such as contain mere than 20 per 

 cent, of carbonate of linic ! Those containing from 5 to IJ per cent, he 

 terms " marly soils ;" and all containing less than 5 per cent, -are left 

 without any distinguishing term or character in regard to their calcareous 

 constitution. (Johnston's Lectures, p. 233.) According to these designa- 

 tions, there would not be an acre of natural "calcareous soil," or even 

 of "marly soil," in all Virginia; nor will there be, after all that shall be 

 judiciously done by the industry of man in supplying calcareous manure 

 to the soils deficient in that ingredient. 



