ARCHEAN SYSTEM

or PRE CAM BRIAN, the oldest rocks known, of world-wide distribution and varied composition, but consisting chiefly of gnei es and metamorphic schists of enormous thickne . Owing to manifold mechanical deformations, sub-divisions of the system are difficult to outline, and the occurrence of fo ils is extremely rare, so that formerly the term azoic (without animal life) was applied to the rocks. These are frequently altered, owing to regional metamorphism, or mingled with sedimentary and volcanic beds, and penetrated by valuable mineral veins. tion of N.W. Scotland, corresponding to Lauren tian in Canada, and the Dalridian schistose series of Scotland _and Scand in a via, corresponding to N. American Hurian, and the Torrid on i an (Scot.) and Sparagmite (Norway) beds or Keweenawan beds (N. American) are principal subdivisions.