. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 292 THE EEGOLITH made by Messrs. Chamberlin and Salisbury: *^Above, the clay graduates into soil which, outside the valleys, is uniformly shallow. Beneath the soil, the clay loses the dark color of the latter, due to the presence of organic matter, but is for a certain distance downward not unlike the superior portion in texture. The deeper lying clay, where limestone is the subjacent rock, is the most characteristic member of the residuary earth series. It is not like that above, structureless, although, like that, it is wit
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 292 THE EEGOLITH made by Messrs. Chamberlin and Salisbury: *^Above, the clay graduates into soil which, outside the valleys, is uniformly shallow. Beneath the soil, the clay loses the dark color of the latter, due to the presence of organic matter, but is for a certain distance downward not unlike the superior portion in texture. The deeper lying clay, where limestone is the subjacent rock, is the most characteristic member of the residuary earth series. It is not like that above, structureless, although, like that, it is without trace of stratification. It generally shows a tendency to cleave, breaking up into little pieces which are roughly cubical. This is often conspicuous, and especially so on the faces of sections which are thor- oughly dry. In such situ- ations large quantities of the clay in small angu- lar blocks may be removed by slight friction. The size of the cuboids varies, within somewhat narrow limits, from a small frac- tion of an inch to one or two inches in diameter. This cleavage is probably a phenomenon of shrink- age due to drying, as it partially disappears when the clay becomes wet. This structure has given rise to the local name of ^joint' clay, an appellation not alto- gether inappropriate, **Upon drying, this variety becomes very hard and rock-like. It only becomes adapted to serve as soil by surface amelioration, as is shown by the fact that, from the thousands of mineral holes scattered over the southern part of the mining district, the material ejected still lies beside the excavations as heaps of clay, without covering of vegetation, although it has been exposed in most cases for many years. Notwithstanding this fact, the clay, even in its deepest parts, wherever examined, is found to abound in minute perforations. These, in many cases at least, indicate the penetration of rootlets, for the rootlets themselves. Pig. 28.—Showing angular character of quartz particles
Size: 1581px × 1581px
Photo credit: © Central Historic Books / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectpetrolo, bookyear1913
