44 The American Geologist. July, 18&7 
forms the country rock, and between these two points extends 
a narrow portion of Vermillion lake on the shores of which 
are frequent large exposures of the same schist, exhibiting 
beautifully the relation it bears to the igneous rocks that cut 
it. Suffice it to say here that the sedimentary character is 
perfectly evident everywhere, even to the very contact with 
the igneous granite, and this fact was specially noted, on the 
occasion of the last visit, by all the members of our party.* 
It may be of interest to mention, also, that two epochs or 
ages, of igneous intrusion upon the schists were noticed. This 
is true both for granitic dikes and for trap dikes ; and the fact 
was noted at two or three miles from the granite boundary, 
and at several places. 
Going northwestward from the commencement of the mica 
schist, one notices the increase in the crystalline character of 
the schist, and in the number and size of the granitic dikes. 
The critical point for observation is found, however, just as 
the transition occurs from schist to gneiss, and to granite. 
The point to which I wish to direct your attention especially 
is on the west side of Outlet bay, on the dull point which em- 
braces the corners of sections 13, 14, 21 and 32, T. 63-17, and 
along the shore of the lake for half a mile westward. This 
shore was examined by the writer in 1887, and although at 
that time the same general conclusions were arrived at as to 
the genesis and succession of the rocks, the examination was 
more cursory, and the conclusions were held in abeyance until 
further and more detailed examination could be made. This 
seemed to be required by the published views of some geolo- 
gists who have questioned the banding seen frequenth' at the 
points of transition from crystalline schist to gneiss, and who, 
like Lawson, have attributed the banding of the gneiss at such 
transitions, to lateral intrusion of igneous dikes along the 
strata planes of a mica schist. The results of this first ex- 
amination are given briefly in the fifteenth annual report of 
the geological survey (pp. 293-94). 
In reviewing the situation the following were found to be 
the structural features which are not compatible with the idea 
*The memhiers of our party were, besides the writer. Dr. U. S. Grant, 
A. H. Elftman, and H. F. Bain, the last a member of the geological 
corps of Iowa. 
