THE GEOLOGICAL SECTION OF MICHIGAN 689 
heavy conglomerates at the top, we get 4,250 feet for the sediments 
alone—conglomerates and sandstones of very rapid deposition for 
the most part. A detailed section is given in the Black River Report, 
Annual for 1906, p. 400. Fairly persistent (Isle Royale, Black 
River, Keweenaw, Mamainse) appear to be the following divisions of 
the Keweenawan from below: 
1. Bohemian range group (Irving’s (1) and (2), Plate XVII) char- 
acterized by numerous flows of labradorite porphyrite type and 
felsites near the top and frequent intrusions, of straight-walled dia- 
base dikes, of felsite, of gabbro and affiliated red rocks, or gabbro 
aplites. North of Bessemer, the thickness, igneous sills included, 
There may not be 500 feet of sediment. 
2. Central (Mine) group.—tIncluding the ‘‘ Greenstone group,” the 
‘‘Phoenix Mine group,” etc., but only a part of Pumpelly’s “ Portage 
Like series,’’ and just about that part included and well exposed 
in the workings of the Central mine on a cross-fissure, exposing a 
good section, examined by Pumpelly and Hubbard, and more re- 
cently supplemented by diamond-drill cores on the same property 
(sections 24, 25, 30, T. 58 N., R. 31 W.). This is a new name we 
would introduce and define as extending from the Bohemia con- 
glomerate, Marvine’s conglomerate (3) or (8) to the “St. Mary’s 
epidote,”’ a sediment, volcanic ash, just above the ‘‘Greenstone”’ and 
Marvine’s conglomerate (15). Characterized by very heavy flows of 
ophite, some of them hundreds of feet thick, so that, for instance, the 
“Greenstone,” the one at the top of the series, extends beneath Lake 
Superior, from one side to the other; often proportionately coarse 
grained. 
On Black River there are possibly 25,000 feet aes flows. 
At aie Lake (7,882), say 8,000 feet. 
. “Ashbed” group.—This group has been named from the Ash- 
vet Mine, or really originally from a lode so called by the miners, 
worked at that mine, Marvine’s (a) and (bd), Irving’s (5) and (6). 
Including conglomerates 16 to 18, characterized by frequent glomer- 
ophyric that is relatively feldspathic and fine grained flows. 
inuthtemlamm@anaclke@shaitss <o:s ihc ee bee soe Or ler ee seceuere 2,400 ft. 
The amount of well-marked conglomerate is not over 50 feet but 
