154 Con/jlomerates in Gneissic Terranes — A.WrnchelL 
as the "Bass wood granite," and the more southerly, as the 
"White Iron granite" — these taking their names from the 
lakes whose shores they occupy.* 
Of the lithok)gical characters of these granites it is not pro- 
posed to speak particularly at present, nor of their structural and 
inineralogical relations to the crystalline and the earthy schists 
which lie along their borders. It may have a bearing however, 
on the object of the present article, to state that the Saganaga 
gneiss holds hornblende for its dominant dark mineral. The 
same is true of the White Iron gneiss, though augite sometimes 
usurps the place. The Basswood gneiss is chiefly micaceous, 
and the mica ranges from muscovite to biotite and hydromica. 
Not unfrequently however, a hornblendic constituent inter- 
venes, and this is sometimes replaced by a viriditic mineral. A 
chloritic constituent often appears in all these gneisses, more or 
less blended with the feldspars. As usual the feldspar is 
chiefly orthoclase; but generally, a small proportion of plagio- 
clase can be seen. In the Saganaga gneiss the quartz individ- 
uals are generally of very large size. 
[t will have a bearing also, on the interpretation of the 
jjhenomena which I propose to describe to state that between 
the gneisses and crystalline schists no structural discontinuity 
anywhere appears— -a gradual transition in mineralogical and 
stratigrapliical characters being everywhere apparent.f Nor is 
there any abrupt break between the crystalline schists and the 
earthy or semi-crystalline schists; and consequently, no such 
phenomenon as a contact between crystalline and uncrystalline 
terranes is known to occur. Nor do I find any uncouforma- 
bility between the proper and very distinct bedding of the earthy 
schists and the foliation of the crystalline schists and gneisses. 
It could not be expected under these circumstances, that any of 
the phenomena of local metamorphism should occur along the 
zone of gradual transition from the crystalline rocks to the un- 
crystalline. 
*Sixleenth Annual Report Minn. Geol. and Nat. Hist. Suro., pp. 3ij0-334. 
These three gneissic or granitic areas appear to be discriminated by Irving 
in his "Preliminiiry Geological Map of the Northwest," in the Fifth An- 
nual Report, U.S. Gaol. Surv., p. 181. 
t These facts have been fully set forth in the XVth and X Vlth Annual 
Reports of the G<;ol. and Nat. Hist. Suro. of Minn., to which refereace may 
be made. 
