'212 The American Geologist. October, 1895 
follows, but at the same time not a chronologic fraction of ei- 
ther as a faiinal zone. Within the Taconic area are included 
th(^ ui)])er iron-hearing rocks of Minnesota, which in Michigan 
and in some parts of Wisconsin are so closely folded with the 
rocks of the lower iron-bearing series that they have neA'er 
before been mapped separately in those states. The attempt 
here made to separately indicate them must be considered, 
therefore, as only a ver}^ general provisional mapping.* 
Areas designated G show the additions which were made to 
the land area by the elevation of those rocks which immedi- 
ately followed the eruptive Keweenavi^an and yet preceded the 
base of the Lower Silurian — i. e. up to the bottom of the 
Trenton limestone. These are distinctively the "Upper Cam- 
brian" of the region and are the only rocks which in the final 
Minnesota reports have been mapped as Cambrian, the Lower 
Cambrian having been called Taconic. 
The foregoing presentation of comparative facts of struc- 
ture, lithology and paleontology, as expressed on the accom- 
panying map, render the following conclusions both reason- 
able and prol)able : 
1. The rocks of the Cortlandt series (the elastics), of the 
original Taconic area and of the upper series of the Adiron- 
dacks, are of the same age. i. e., Taconic or Lower Cambrian. 
2. The basic rocks of the Norian or Upper Laurentian sys- 
tem of Canada are of the same age as the gabbros of the 
Adirondacks. 
3. The Taconic in America embraces all the strata contain- 
ing any known fossils older than the Dicellocephalus zone, or 
Upper Cambrian. It is separated from the Archean by a 
profound non-conformity. 
4. The Animikie strata in Minnesota and in general the 
upper iron-bearing series of the Lake Superior region are of 
the age of the Taconic. 
5. There are great objections to the supposition that the 
Taconic age is represented in the Lake Superior region b^^ a 
supposed erosion-interval between the red sandstones of the 
Upper Cambrian (St. Croix or Dicellocephalus zone). 
*Van Hise's map of the Penokee series accompanying the Monograph 
on the Penokee Iron-beai'log rocks of Michigan and Wisconsin (Men. 
XIX, U. IS. (ieol. Survey) has been jjiiblished since this map was con- 
structed. It would not, however, essentially modify it. 
