Ladogian Series

(named after Lake Ladoga), one of the Precambrian series. It was identified by the Finnish geologist J. Sederholm in 1897. On the bottom it is composed of amphibolite shales, amphibolites, metaeffusives, and marbles; on the top are biotite shales and biotite-quartzes. Some varieties of dark-colored shales with strata of coarse detritus resemble slaty formations. The Ladogian series is cut by granites that are 1,950,000,000 years old.