294 J. P. Kimball on Iron Ores of Marquette, Michigan, 
general distribution, connected with the fact of its coéxtensive 
association with metamorphic sedimentary strata, tends in this 
instance to invest the intrusive granite with characters distinct 
from those of its greater development, and to impart to it the 
special phenomena of an independent dyke. Apart from the 
evidence of superposition, the lithological features of the Gran- 
ite Belts, so far as they have been indicated, bear a marked anal- 
ogy with the standard characters of the Laurentian series as de- 
termined in Canada and upon the north shore of Lake Superior, 
In a private letter from Mr. T’. Sterry Hunt, acquainting me 
with some of the unpublished leading results of Mr. Murray's 
examinations upon the south shore, 1 am informed that this geol- 
ogist, whose opportunities for comparison cannot be too highly 
appreciated, describes the islands and some points on the main 
land north and northwest of Presqu’isle as of Laurentian gneiss 
with hornblende, epidote, and pyroxene, arriving at this conela- 
sion through the observation to the south of these points of the 
greenish slates, greenstone, dolomitic limestones and conglome 
rates, associated with the beds of iron ore, and their relations to 
the gneiss. This latter series he judges to be the equivalent of 
the Lower slate conglomerate, or chloritic slates, at the base of 
the Huronian system, regarding them here as retaining a 
the same relative conditions as upon Lake Huron where the dol- 
omite marks the division between the Upper and Lower slate 
conglomerates. 
The gneiss which marks the boundary of the granite belts, 
and accordingly characterizes the top of the Laurentian series 
in this region, the same as it is elsewhere represented, is suc- 
ceeded by dark colored hornblendie schists, which consequently 
represent the base of the Azoic or Huronian series. These 
schists are followed by a series of augitic rocks and schists, m- 
shade, resembling in this particular the Lower slate = re 
which they seem to differ only in the absence of bles and 
boulders from the subjacent Laurentian rocks, which there oe 
a distinguishing feature. Messrs. Foster & Whitney, cng 
describe as occurring upon Little Presqu’isle a pure white 
Spar containing acicular crystals of hornblende, passing — 
arate beds of each of these component minerals, and enclosi 
