122 THE JOURNAL OF GEOLOGY. 



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 Menom- 

 inee, 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, extend- 

 ing 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 



