. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. SEDENTARY MATEEIALSi EESIBUAEY DEPOSITS 297 Delaware and southwestern Pennsylvania are mainly decom- posed, MgMy feldspatliic, gneissic rocks, which as dug from the pits still retain their gneissic structure, but are now plastic clays full of angular quartz fragments, mica scales and feldspar par- ticles in various stages of decomposition. The change that has taken place consists in a kaolinization of the feldspars, whereby the alkalies are largely removed, and a residue consisting essen- tially of a hydrous silicate of alumi
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. SEDENTARY MATEEIALSi EESIBUAEY DEPOSITS 297 Delaware and southwestern Pennsylvania are mainly decom- posed, MgMy feldspatliic, gneissic rocks, which as dug from the pits still retain their gneissic structure, but are now plastic clays full of angular quartz fragments, mica scales and feldspar par- ticles in various stages of decomposition. The change that has taken place consists in a kaolinization of the feldspars, whereby the alkalies are largely removed, and a residue consisting essen- tially of a hydrous silicate of alumina left in their place. The quartz gran- ules are disaggregated, and their surfaces some- times slightly etched by the action of the alkaline carbonates; the black mica, where such existed, decomposed, giving rise to rust-colored spots. The material is dug from the pits and washed with water to separate the im- purities, the "kaolin" or elay remaining in suspen- ^f , on the left, the mineral ^ ^ kaolmite as seen under the microscope,. and on the right, washed kaolin. sion, and being ultimately saved by filtration through canvas. This finest material, as seen under the microscope, still contains particles of undecomposed feldspars and shreds of white mica, together with other extremely irregularly outlined, some- times almost amceba-shaped forms, as shown in Fig, 29. An average of two mechanical analyses of this clay, made under Dr. Whitney's direction, yielded the results given below: Moisture in Air- Dry Material at 100'^ 0. MoiSTtrEE ON Ignition Silt . MM. Fine Silt . MM. Clay . MM. 0/, % % , Chemical analyses of the same material, made in the laboratories of the United States Geological Survey, yielded:. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectpetrolo, bookyear1913
