The salient points of the thesis are summarised as follows. 1. The first chapter is essentially a review of chemical and mineralogical transformations accompanying the weathering of some primary rock forming minerals, and includes a discussion of feldspars, trioctahedral and dioctahedral mica, quartz, chalcedony, opal, metamorphic, accessory, and opaque minerals, and ferromagnesian minerals. Included therein is a hypothesis for the mechanism of formation and layered structure of hydrobiotite. 2. A brief review of the geology, geomorphology, <and age of weathering in north east Scotland is presented in chapter 2. 3. The geology, field work and laboratory investigations of the weathe~ing in a meta-sediment, a quartz-mica-schist, and the Tertiary gravels at two sites, are presented in chapters 4, 5, 6 and 7 respectively. Some features found are considered to be relic, and formed under previous conditions. The weathering products include 2:1 type and kaolin minerals. 4. Secondary silica in a minute form was found to be common and is referred to as "aphanitic silica". The main optical properties and occurrence have been noted. 5. Secondary deposits of Ti02 (leucoxene) are also common, and because of the great opacity of Ti02, may be very ;caospicuous in thin sections even though actual concentrations are very low. Some of the leucoxene is shown to contain rutile and anatase. The source of much Ti02 may be biotite, and very rarely Ti02 may apparently completely pseudomorph biotite. 6. A comparison of the kaolin minerals (poorly ordered kaolinite, well-crystallised kaolin'ijte,and halloysite) from some sites has been made by a variety of techniques including thin sections, X-ray diffraction, DTA, infrared spectroscopy, chemical intercalation, and electron microscopy. Some problems in the study of these clays are considered, particularly with respect to monomineralic and polymineralic mixtures. It is concluded that there are fundamental differences between the structures of kaolinne and halloysite, other than the occurrence of interlayer water in the natural state of halloysiteamphiboles and pyroxenes (generally), tremo1ite-actino1ite, and accessory minerals in the weathered materials is discussed and summarised. 8. The age of weathering and the contribution of weathering products to contempotary soils is assessed from a consideration of the evidence found and that available. It is concluded that in north east Scotland contemporary weathering has very little effect upon weathered rocks beneath soils