262 



SCIENCE. 



[N. S. Vol. IV. No. 87. 



Our district being without tlie limits of 

 the glaciated areas possesses a soil which 

 has been in process of formation during 

 many periods. It has never been disturbed 

 by either marine or lacustrine agencies, and 

 consequently, is but the residual material 

 accumulated on the surface of the lime- 

 stone rock after the decay of higher strata. 

 These strata consisted of the coarsely crys- 

 talline, crinoidal Burlington limestone and 

 abounded in layers of white chert. 



The surface stratum of the soil which we 

 are now considering is a layer of angular 

 white chert gravel. The pieces vary in size 

 from very small to a cubic foot, but sizes of 

 a cubic inch to ten cubic inches predomi- 

 nate. Where the ridges are narrow the 

 surface is so completely covered with this 

 broken chert that the true soil cannot be 

 seen, and in the spring, when the brown 

 oak leaves and dried prairie grass are 

 burned off, the hills look like hugh piles of 

 broken rock. On the steeper hillsides the 

 chert layer, which is here a true talus, is 

 often several feet in thickness, and no at- 

 tempt is made to reach the underlying soil 

 for the purpose of cultivation. But on the 

 flat-topped ridges, the plow passes under 

 the superficial chert into a rich black soil, 

 which is six to eight inches in thickness 

 and remarkably fertile. This soil layer is 

 nearly free from large fragments of chert, 

 although very small particles abound and 

 aid in giving the soil a very loose texture. 

 The black color is, of course, derived from 

 the decay of vegetation, and the carbona- 

 ceous matter accumulates more rapidly 

 where the overlying chert layer is thickest. 

 In fact, the existence of a black soil in this 

 latitude is probably largely due to the pres- 

 ence of the chert. 



Several years ago a ' cyclone,' in passing 

 across the hill tops in the vicinity of 

 Eancho Springs, in Stone county, prostrated 

 the timber in narrow belts. The fallen oaks 

 have upturned the soil, producing fine sec- 



tions through it. Under the dark soil layer 

 we find a light yellow clay, at first nearly 

 free from chert, but which, at the depth of 

 two feet, contains such a large percentage 

 of large chert fragments that it requires the 

 use of the pick in excavating it. This yel- 

 low sub-soil is a stiff clay and, when puddled 

 with water and plastered into the * chink- 

 ing ' between the logs of the simple country 

 houses, makes an excellent substitute for 

 mortar. When plowed into, rained upon 

 and dried, it hardens on the surface as 

 though frozen, so that to walk over a 

 plowed field when it is in this condition 

 makes no impression on it. Yet it con- 

 tains the elements of fertility and in time 

 will weather into a good soil. 



The yellow subsoil clay grades imper- 

 ceptibly downward into a bed of closely 

 packed but invariably fragmental chert. 

 At three feet from the surface of the soil, 

 less than 10% of the material is clay, occu- 

 pying the narrow crevices among the chert. 

 At this depth also the yellow clay changes 

 rather abruptly to a similar fine-grained 

 stiff clay of a bright brick-red color. From 

 here to the surface of the limestone rock, 

 which may be 10 or 20 feet from the surface 

 of the soil, the mass is composed almost 

 exclusively of the fragmental chert. What 

 clay there may be among it is always of 

 the bright red variety. 



ISTow it is to the characteristic feature of 

 the subsoil clay, viz., its color, that I wish 

 to call special attention. This, as we have 

 just seen, differentiates naturally into an 

 upper yellow variety and a lower red va- 

 riety. The line of demarcation between 

 them is not sharp, and bears no definite 

 relation to the main body of the chert. For 

 when the ridges are broad, and the subsoil 

 clay over the chert bed thickens, the surface 

 of the clay rises into the subsoil stratum^ 

 leaving quite a thick bed of not very stony 

 red clay over the main body of the chert. In 

 short, as the line of demarcation persists in 



