Bruce Series

Division of Precambrian rocks in North America that is well-developed northeast of the Lake Huron region (the Precambrian began about 3.8 billion years ago and ended 540 million years ago). The Bruce Series is the lowermost of the three major divisions of the Huronian System; it overlies pre-Huronian schists, underlies rocks of the Cobalt Series, and consists of about 1,500 m (about