Elements of structural geology / Элементы структурной геологии

The special province of structural geology among the branches of geological science lies in the recognition, representation, and genetic interpretation of rock-structures. Without for the moment defining precisely what is meant by rock-structures, let us consider any geological cross-section showing beds in various attitudes — flat-lying or inclined, folded or faulted — perhaps in places intruded by igneous rocks or covered with lava-flows, and again in places metamorphosed. Such a section shows the shape and attitude of the various rock-units present, and is said to represent the geological structure of that part of the earth, in the plane of the section. The shapes and attitudes of the several rock-units shown, as they now exist in the earth, are the result firstly of processes connected with their original formation when their primary structures were developed, and secondly of all later processes whether of mechanical deformation or chemical reconstitution, that have affected them. It is usual to distinguish those effects that are connected with the later stages of the formative processes of sedimentary or igneous rocks as penecontemporaneous, since they are intimately connected with the conditions hat obtained during the origination of the rock in question, while structures of entirely subsequent formation are regarded as secondary. Uplift, tilting, faulting, or folding in general give rise to secondary structures, but although it is true that structural geology is very largely concerned with these, it is also clear that one must have a very good understanding of the objects that were thus deformed, and that attention must be devoted to the primary and penecontemporaneous structures of rocks before proceeding to treat with their secondary deformation. <...>