CONGLOMERATE

in business, corporation formed by the acquisition by one firm of several others, each of which is engaged in an activity generally unrelated to that of the original. The management of such a corporation may wish to diversify its field of operations for a number of reasons: making additional use of existing plant facilities, improving its marketing position with a broader range of products, or decreasing the inherent risk in depending on the demand for a single product. There may also be financial advantages to be gained from the reorganization of other companies. Conglomerate mergers are a 20th-century phenomenon, with the greatest number occurring after World War II. The practice became widespread especially in the 1960s and the 1980s. in petrology, lithified sedimentary rock consisting of rounded fragments greater than 2 millimetres (0.08 inch) in diameter. It is commonly contrasted with breccia (q.v.), which consists of angular fragments. Conglomerates are usually subdivided according to the average size of their constituent materials into pebble (fine), cobble (medium), and boulder (coarse). Classification of conglomerates is based on the range of lithologies represented in pebbles, degree of size-sorting, and composition of matrix. Each of these criteria has genetic implications. There are two broad types of conglomerates: (1) those whose pebbles are generally of one lithology, well-sorted (i.e., narrow size distribution), and matrix-poor; and (2) those with a heterogeneous pebble lithology, poorly sorted, and with abundant matrix. The degree of sorting indicates the method of deposition. Well-sorted conglomerates are produced by normal water currents, whereas the poorly sorted varieties result from rapid deposition, as in the case of mudflows or subaqueous slides. Well-sorted conglomerates imply erosion and deposition over a long time period with a loss of unstable minerals and a rock dominated by quartz or chert pebbles; the geologic environment of deposition is usually a widespread basal formation of overlapping marine units. The poorly sorted conglomerates have a matrix of clay or sand and, by analogy with sandstones, are termed graywacke conglomerates. The abundance of unstable minerals with poor sorting indicates rapid mechanical erosion and deposition, as in alluvial fans or in density currents (i.e., highly turbid bottom currents) resulting from gravity flows. In contrast to well-sorted conglomerates, formations are usually thick and of limited spatial distribution. Deposition by ice either in glacial till or by ice rafting also produces poorly sorted conglomerates.