Page:The Journal of geology (IA journalofgeology11893univ).pdf/136
which are correlated with the Upper Huronian have not the same successions of formations as in these districts. The Upper Huronian north of Lake Huron has a set of formations which can not be correllated with the formations above given; the same is true of other series to the south which are here placed. The position of these latter as a part of the Upper Huronian must not be considered as a question finally determined, but rather as representing the probability, from the weight of evidence at the present time. It can not be expected that in a great geological basin the same subordinate succession of formations will be everywhere found.
However, for the present, regarding all these series as Upper Huronian, this is the most widespread of the Lake Superior pre-Cambrian sedimentary series. It includes a great area, extending from the Sioux quartzites of Dakota on the southwest, to the Huronian rocks north of Lake Huron on the east, and thence far to the north, and from Lake Huron to the Animikie series of the National Boundary west of Lake Superior. Within this area are included the major portion of the Baraboo quartzites of Wisconsin; the major portion of the large area in the Upper Peninsula of Michigan, the eastern arms of which are the Menominee, Felch Mountain, and Marquette iron-bearing districts; the greater part of the Penokee-Gogebic iron-bearing series of Michigan and Wisconsin; the Chippewa quartzites of Wisconsin; St. Louis slates of Minnesota including the newly developed Mesabi range of Minnesota, and the Animikie series of Thunder Bay, Lake Superior and its westward extension. That most, and perhaps all of these areas were once connected, there can be no reasonable doubt.
This broad semicircular zone of Upper Huronian rocks, extending from the National Boundary west of Lake Superior through Ontario, Minnesota, Michigan and Wisconsin, to the north Channel of Lake Huron, and thence north to the east side of James Bay, suggests that the transgression of the sea was from the south and east, and that the source of the mechanical detritus is the great expanse of so-called Laurentian rocks west of Hudson