1890.] Proceedings of Scientific Societies. 291 
THE CRYSTALLINE SCHISTS OF THE BLack Hilts or Dakota. C. 
R. Van Hise, Madison, Wisconsin.—A review of the distribution of 
the slates, schists, and granites is given as mapped by Newton. Cross 
lamination, and the arrangement of pebbles in the conglomerates, show 
that the real thickness of the slates is independent of their apparent 
thickness as measured by cleavage. The largest area of crystalline 
schist is a belt surrounding the granite mass in the southern part of 
the pre-Cambrian area. It always strikes parallel to and dips away 
from the granite. The structure is then here laccolitic. The granite, 
by its contact and dynamic action, produced these crystalline schists. 
The evidences of fragmental origin in clastic rocks is generally re- 
tained when subject to pressure only, however great the pressure. 
The evidences of fragmental origin in clastic rocks is rapidly obliter- 
ated when they have been subject to dynamic action, Tlustrations : 
The original detritus of the Black Hills mica-schist was feld sparand 
quartz. By a decomposition of the former, producing mica and quartz, 
and a breaking down of the larger particles of the latter by dynamic 
action, coarse, even granular, completely crystalline mica schists have 
been extensively produced. Different degrees of crystalline character 
are seen in the field, and various stages of the change are traced out in 
thin section, The paper then speaks of the age of the slates, schists, 
and granites. r4 
Some RESULTS OF ARCHEAN STUDIES. By Alexander Winchell, 
Ann Arbor, Mich.—This memoir is a condensed statement of observa- 
tions made by the author in northern Minnesota and contiguous 
regions. With these are incorporated some records of other observers 
in the same field. Being simply a report of facts observed, the memoir 
is calculated to stimulate inquiry rather than provoke discussion. The 
field is thought to be one of such comparative simplicity of structure 
as to promise a much easier solution of the Archean problem than 
any of the complicated regions of New England and eastern Canada. 
Several systems of rocks are enumerated in succession, distinguished 
by structural relations, and lithological and mineralogical contrasts. 
These are, in descending order: V. The uncrystalline schists (Anim- 
ike): IV. The sub-crystalline schists (Kewatin of Lawson) ; III. The 
crystalline schists (Vermilion of N.. H. Winchell); II. The gneissoid 
rocks; I. The granitoid rocks (not fundamentally distinct from the 
gneissoidy. The oldest four of these systems exhibit an unexpected 
-stratigraphical conformity with each other, and a stratigraphical and 
mineralogical intergradation, which seems to unite them in closer 
. 
