The Residual Deposits

Abstract

The residual deposits are the insoluble products of rock weathering which have escaped distribution by transporting agencies, and which still mantle the rocks from which they have been derived. Their components belong to two classes, namely, unaltered minerals from the original rocks, and the insoluble products of decomposition. The nature of the minerals of the first class depends upon that of the bedrock, but quartz, felspars, and muscovite are amongst the commonest, although the felspars are usually much decayed. The rarer durable constituents of rocks, such minerals as zircon, rutile, garnet, tourmaline, kyanite, etc., and various iron oxides, magnetite, hæmatite, ilmenite, and chromite, are also to be found. The silicate minerals comprised in the second class are chiefly hydrous aluminium silicates of the kaolinite-halloysite group, hydrous magnesium silicates of the serpentine-talc group, chlorites and hydromicas, zeolites, and the epidote minerals. Various hydrated oxides of iron and aluminium, and colloidal silica, may also be present.