The Algonkian sediments of western Shansi are represented by a sedimentary and eruptive formation of very great thickness. They consist of coarse and fine groined sandstones, generally of reddish brown and white colour, interbedded with inconsistent coarser and finer conglomerate layers and reddish brown shales. The formation is intruded by diabases, occuring partly as vertical or oblique dikes, and partly as intrusive or effusive sheets.