A discussion of geological description and an account of the Descriptive System LSDØ2 are given. It is shown that by examination of the aims of description and of its main instrument, the geological observer, a set of principles and objectives may be established in order to design descriptive systems. The application of these principles is demonstrated by an account of the theory and practical aspects of the Lithostratigraphic Descriptive System LSDØ2.

Mantle diapirism centred in Transylvania is suggested as the explanation of the Carpathian Arc and the Pannonian Depression, deviation of the Danube from a formerly straight course, and the trends of the Eastern Alps and horsts and troughs in the Bohemian Massif and Poland. Central location in Transylvania is at the crossing-point of deep fractures, parts of great circles, most conspicuously displayed in Transcaucasia and along the Zagros Main Thrust line. Mantle diapirism extended westward from Transylvania along each lineament in Hungary. Pannonian deep lithosphere may be a subcrustally thinned extension of the Bohemian Massif, with a relict unthinned fragment appearing as the Dobrogean Massif. This extended massif would originally have lain almost parallel to the western boundary of the Russian Platform and to the present Dinaride belt.

An occurrence of small diagenetic siderite concretions is described. They occur towards the top of a postulated shallowing sequence of cleaved Lower Palaeozoic siltstones and shales. The concretions occur as lenses and aggregates associated with horizontal grazing trails, and also as diffuse bands apparently unrelated to the latter. The concretions are compared with other similar structures described elsewhere, and an origin by diagenetic growth beneath the sediment–water interface in a marine environment is postulated.

In northern Snowdonia welded ash-flow tuffs, correlated with the Pitt's Head Tuff Formation occur intercalated with Caradoc shallow marine shelf sediments. Within the tuffs there are vent-like structures which have a diapiric form where fiamme are drawn in towards a central core. The cores may have a constrictional linear fabric of streaked out fiamme, or may consist of vitrous tuff surrounded by a zone of buckled planar fiamme. There are associated zones of quartz nodules which are thought to represent quartz filled vesicles. The diapiric structures are believed to be rootless vents. Steam generated by the heat of the flow in contact with shallow water is thought to have caused explosive disruption of the tuffs as consolidation and welding occurred. These structures are thus themselves indicators of deposition of ash-flow tuffs in a shallow water environment.

Evidence is presented that some fibrous veins may be formed by recrystallization of the original rock in place. It is suggested that water in a joint promotes pressure solution of the adjacent wall rock. Redeposition under conditions of tensile strain crystallization causes growth of crystal fibres into the joint and into the wall. The effects of this process are revealed by reference to fibrous veins that are present in the laminated, dolomitic, quartz sediments at Mount Isa Mine.