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1884.] The Crystalline Rocks of the Northwest. 985 
Minnesota. Until very recently it has been the practice of geol- 
ogists, almost without exception, to refer every crystalline rock 
inthe Northwest either to the Huronian or to the Laurentian. 
Thus, when the survey of the State of Michigan was reinaugu- 
rated in 1869, the geologists of the upper peninsula were com- 
pelled to choose between a confession of their inability to estab- 
lish the age of the rocks they were studying and the adoption of 
some of the recognized designations, In Wisconsin the case 
was similar, with the additional fact that the Michigan geologists 
were collaborators, The same was true again in Minnesota. 
What more natural than that the Michigan and Wisconsin rocks 
should be found to extend, with nearly the same features, into the 
State of Minnesota, and that their familiar names should at once 
be applied to them ? 
But when on more careful examination, both in the field and 
in the literature of the crystalline rocks, and over a wider extent 
of territory, and especially in the light of more recent researches 
in New England, New York, Pennsylvania and Canada, it is 
found that the nomenclature is imperfect, and furnishes but a tot- . 
tering scaffold to support the workmen of a great and ever- 
Spreading structure, we are thrown into such difficulty and doubt 
that we are prone either to reject the old scaffold and build anew, 
or to clear away the accumulated rubbish about the foundation 
and examine on what basis the old one stands. To-day, how- 
ever, we intend to do neither of these, but rather set forth a few 
of the incongruities and difficulties of the actual situation. 
We are indebted, unquestionably, to the geologists of Michi- 
§an and Wisconsin for the most exhaustive and satisfactory de- 
Scription of the crystalline rocks of the Archean age that has 
yet been published in America, In order that some of the diffi- 
ties of the situation may be made clear, I desire to review 
concisely the broad stratigraphic distinctions of the crystalline 
rocks that have lately been studied in Michigan, Wisconsin and 
Minnesota, By the aid of the published results of the surveys 
of Brooks, Wright, Irving, Rominger, Pumpelly and others, a 
generalized statement can be formulated. To these I shall add 
Such published results and unpublished field observations from 
innesota as may be furnished by the survey of that State, in 
Order that the scheme may cover correctly the crystalline r ocks 
of the entire Northwest. 
