Handbook of Paleontology 201 



sidered equal to that between the Archeozoic and Pro- 

 terozoic systems. The Huronian series consists of a 

 marine series and above this a marine and fresh-water 

 series resting upon an erosion surface and having at its 

 base a glacial boulder conglomerate or tillite, the oldest- 

 known glacial deposit. The two series are composed of 

 quartzites, conglomerates, limestones and graywackes, 

 with a combined thickness of about 15,000 feet in the 

 Lake Huron region. Above the Huronian series, with a 

 break between, is the Animikian or Great Iron Series in 

 which are found the largest and richest deposits of iron 

 in North America. Seventy per cent of the hematite ores 

 found in the Archeozoic and Proterozoic formations of 

 the Lake Superior region occur in this series of rocks. 

 These strata are still for the most part horizontal and 

 from the widely isolated remnants are estimated to have 

 a thickness of 6000 to 14,000 feet in places, the latter in 

 the Penokee area of Michigan. They have a widespread 

 distribution over the Canadian shield. The formation 

 usually begins with a basal conglomerate followed by 

 cherty limestones and dolomites, carbonaceous shales and 

 beds of sandstone. No fossils have been found, but the 

 general character and appearance of the beds points to 

 a marine origin, though some seem to have a continental 

 character. 



The Late Proterozoic is separated from the Middle 

 Proterozoic by a break in the record. The Keweenawan 

 is a series of volcanic and continental formations with an 

 estimated thickness of 50,000 feet of which 15,000 feet 

 are sedimentary rocks. This system is characterized, in 

 contrast to the lower Proterozoic series, by the presence 

 of numerous lava beds, aggregating an enormous thick- 

 ness, estimated at about six miles. Sixty-five distinct 



