ARCHEAN (iir-ke'an ) SYSTEM ( from apxolbs, arehaios, ancient). A name proposed by J. D. Dana, in 1872, for the entire series of crystalline rocks that forms the oldest under lying fundamental complex of the earth's crust. Earlier names applied to this series were Azoie, Primitive, Huronian. and Laurentian. of Ameri can geologists, and Urgcbirge and Primitivge birge of the still earlier Germans, \Verner and Lehmann. The rocks of this system eonsist of a complex series of gneisses, granites, and schists, with a host of associated massive igneous intru sions, all of which have suffered profotmd dis turbances and metamorphism to such an extent that it is extremely doubtful if at the present day there exist any traces of their original characters. They form, as a rule, the cores of the great mountain masses, and are the original sources from which were derived. by erosion through countless ages. all the forms of later sedimentary rocks, which they underlie with marked unconfonnity. Various classifications of
Arehiran rocks have been made in the attempt to organize them into stratigraphic groups, but owing to the complex nature of the series, and to the almost complete absence of reliable data for determining the relative age of the com ponent formations, no one classification has as yet received general recognition. These Ar•m an rocks of undoubted primeval origin, together with certain others, which because of their prob able sedimentary derivation have been separated under the name Algonkian. antedate in respect of the time of their formation the rocks of the Cambrian system. and can lie described to better advantage under the title, PRE-CAMBRIAN FoRmA TIONS, to which article the reader is referred for further information. See also ALGONERN SYS TEM ; and TACONIC SYSTEM.