Review of Recent Geological Literature. 59 
ing to the crystalline rocks of the Northwest, occupying thirty-three- 
pages. 
Professor Winchell reviews the development of knowledge of the 
crystalline rocks of the state during the progress of the present survey, 
and points out some of the problems that need further investigation. 
He notes that the Archean group has been subdivided, sometimes in- 
to only two parts, but more frequently into three or more, which are 
accepted not only by the geologists of the Northwest, but by geologists 
who are at work on this group of rocks throughout America and Eu- 
rope. In Minnesota six members of the group, if this Huronian be in- 
cluded in it, maintain a constancy of character and stratigraphic posi- 
tion extending into Wisconsin, Michigan and Canada, such that they 
require separate descriptions. But Prof. Winchell regards the Huron- 
ian as the equivalent of the Lower Cambrian of Sedgwick, instead of 
which, however, he would adopt the name Taconic, proposed for these 
rocks in New York by Emmons, referring to this series the Animike 
slates north of lake Superior. 
The Laurentian rocks of the Canadian geologists are divisible, as 
shown by Prof. Winchell's observations in the Minnesota survey, into 
three parts, having different genesis and age. They are here describ- 
ed as "partly the result of change in situ from old sedimentary strata 
of Laurentian age, and partly the result of eruptive forces which have 
caused an extrusion and partial overflow over later sedimentary strata 
of some of the fused materials of tlie same old strata. Such extrusion 
has taken place at least at two epochs. * * * " Under this view 
the name Laurentian ought to be applied only to the first of these 
parts, which is the fundamental gneiss ; and the eruptive masses ori- 
ginating from it are of subsequent age, as Vermilion, Keewatin, Ani- 
mike, or later, to be determined by their relationship with these series 
overlying the true Laurentian. 
Next above the gneiss is the great series of crystalline schists named 
Vermilion by Winchell in 1886 and Coutchiching by Lawson. 
The former shows in this report that the Laurentian sedimentary age 
probably ended with a characteristically eruptive era, producing in 
some places an unconformable and elsewhere a conformable transi- 
tion, such as have been observed, from the Laurentian gneiss to the 
Vermilion schists. There is again a gradual and conformable transi- 
tion from the Vermilion to the Keewatin series, the latter having near- 
ly the same characters as about the Lake of the Woods, where it was 
studied and named by Dr. Lawson, and the Keewatin period, accord- 
ing to Prof. Winchell, "closed by a renewal of active eruption as pro- 
found in its energy and its effect on the pre-existing strata as that 
which marked the close of the Laurentian." The vast deposits of iron 
ores, chiefly jaspilyte, which are mined at Vermilion lake, are includ- 
ed in the Keewatin series, but whether the jaspilyte was sedimentary 
or eruptive remains an unsettled question. 
Much diversity of opinions has prevailed concerning the correlation 
