It is proposed in the following pages to give a preliminary
description of certain types of Minnesota rocks, to serve as a framework for a more complete discussion of the same in the final report.
The field relations and to some extent the microscopic characters of the rocks described in the following pages have been given by the state geologist in the annual reports for 1879, 1880, and 1881, and in volume I of the final report. In some cases it will be found that the field relations have led the state geologist to different conclusions concerning the nature of the rocks in question from those adopted by the writer, who has based his views upon the correlation of the microscopic characters of rocks and their field relations, as studied by him elsewhere.
NOTE.-The work embodied in the following report by Dr. Wadsworth was done in 1886, in
the laboratory of the survey at the University of Minnesota. It should strictly be considered part of the annual report of progress for that year. But in accordance with the terms of a recent law of the legislature, and because that volume would be unduly swollen if this were included in it, this contribution to the progress of the survey is herewith issued as one of the Bulletins of the
Consistent with the practice of the survey, though not in accordance with that of Dr. Wadsworth, the spelling of rock names is made in 'yte', in order to distinguish them from mineral names in 'ite'. This distinction was proposed by Prof. J. D. Dana, and serves well the purpose for
which it was instituted. N. H. WINCHELL.
Bulletin No. 2. Preliminary Description of the Peridotytes, Gabbros, Diabases and Andesytes of Minnesota.
Minnesota Geological Survey.
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