In pursuit of the factors taking part in weathering of the granitic rocks, several regions have been picked up and topographically researched with respect to the weathered state, while, on the other hand, the inner-structure variations of biotite obtained successively from landsurface to seemingly unaltered rocks lying in the depth in the related areas have been röntgenometrically compared with one another. Emergence and growth of choritic mineral in certain specimens have, though even microspically not identifiable, been noticed in accordance with grade of weathering.