THE OUTER CONGLOMERATE—THE BOHEMIAN RANGE. 179 
Eagle River section. They are the typical fine-grained diabases, having a 
grain whose highly crystalline nature can yet be distinctly seen with the 
naked eye. In the compact portion, which forms much the greater part of 
each bed, the color is usually a dark brownish-gray to black, withalight shade 
in more altered layers. Some beds show numerous minute dark-green spots 
of chlorite, dotting the surface of the fracture. These lower portions have 
often a strong tendency to a columnar structure, much more marked than 
usually seen on the South Shore, though not nearly so striking as that often 
to be observed on the Minnesota coast. The amygdaloids are very thin, 
and have usually a dark reddish-brown, tough, aphanitic, often very hard, 
at times soft and earthy, matrix, with abundant calcite and laumontite. These 
amygdaloids show often a sort of rude stratified appearance of the same 
nature, though not so pronounced, as that of the stratified amygdaloids of 
the vicinity of Agate Bay on the Minnesota coast. The typical structure 
of the diabase flows of the Keweenaw Series is here most beautifully shown, 
each bed, with its thick, massive, columnar lower portion, and its thin, pecu- 
liar, slaggy upper portion, standing out sharply from the adjoining layers. 
Agates occur quite commonly as sparsely scattered amygdules in the mid- 
dle and lower portions of the beds. 
Kast of Agate Harbor the whole thickness of these upper diabases 
comes in—some 1,500 feet—and continues to the end of the point, being 
overlaid in all this distance by an outer conglomerate, the base of the Upper 
Division of the series. This Outer Conglomerate forms the greater part of 
Manitou Island, to the east of Keweenaw Point. 
As in the section south from Eagle River, so in the more easterly part 
of Keweenaw Point, the exposures in the median valley south of the mines 
under the Greenstone are infrequent. Enough is seen, however, of these 
covered belts where they reach the shore of Béte Grise Bay, to prove that 
they are made up of the usual fine-grained diabases and amygdaloids with 
rarer luster-mottled melaphyrs and porphyry-conglomerates. 
The Southern or Bohemian Range, however, shows in the vicinity of 
Lac La Belle many interesting exposures. The rocks of which this range 
is made up have been described as wholly different from those of the more 
northern belts, and have even been regarded, by more than one authority, as 
