Conglomerates m Gneissic Terranes- — A. Winchell. 261 
micaceous, but also a very marked mechanical change, which 
is most apparent in the deformation of the pebbles of the con- 
glomerate." "The fragmental nature of the conglomerate and 
the deformation of the pebbles are, in both regions, indisput- 
able facts." 
Even the great lenticular masses of the granite are not rec- 
ognized by Crosby as eruptive. Though they sometimes 
branch and enclose masses of schist, the concomitant conditions' 
are such as to furnish "a complete refutation of the view that 
these masses are eruptive." "True eruptive granite is proba- 
bly entirely wanting in the Black Hills." 
The geological conditions appear to be similar tothose along 
the international boundary in Minnesota and Canada ; and pro- 
fessor Crosby's conclusions appear to be entirely accordant 
with the facts. 
Quite recently an important memoir has been issued liy 
Dean F. R. Carpenter.'' The conditions as found in Minne- 
sota are accurately described in the account of the Black 
Hills, quoted from the report of N. H. Winchell : "The mica 
schists become more and more granitic by interstratification, 
yet the schist maintains its distinctive character, and pre- 
vails up to the very base of the granite ; and appears in thin, 
contorted lamina? in the granite itself." ' To these and simi- 
lar views he assents. In the further details he is quite in ac- 
cord with professor Crosby, and reaches the same conclusion 
in reference to the probable metamorphic history of the crys- 
talline terranes. 
Now that attention is particularly directed to the existence 
of water-worn pebbles and fully formed conglomerates in 
gneissic terranes, both of post-Laurentian and of Laurentian 
age, it is quite probable that many additional occurrences 
will be pointed out, and that the evidences of an early sedi- 
mentary history for most of the granitoid and gneissoid rocks 
will rapidly accumulate. 
'' Preliminary Report of the Ddkoia School of Miiie>< upon Ueolo(jij. 
Mineral Resources and Milh of the Black Hills of Dakota. Rapid City. 
1888. This was reviewed in the March number of tlie GEOi>of;i.sT. 
' J^ud\o\Y'i< Report of a Reconnaissance of the Black Hills of Dakota,. 
1874, p. 42. 
