20 J.D. Whitney on Minerals of the Lake Superior region. 
of the Minnesota mine, at a depth of from 70 to 80 fathoms, was 
calcite. Traces of what appeared to be laumontite were notic 
along the selvages of the lode, which at this depth is quite as 
rich in copper as anywhere above, but the lode seemed to be 
very compact in its texture and no other zeolite was seen in it. 
entire, or almost entire, absence of some of the more com- 
mon Geclises ‘from the Lake Superior region is worthy of notice. 
Those minerals which are most characteristic of the Nova Scotia 
ean rocks are almost entirely wanting on the Lake. Neither 
= seh or heulandite have ever been observed and me 
r region, on the south shore of the Lake.* The 
. of lithological character between the traps of Nova 
Scotia and those of Lake Superior, which has frequently been 
urged as a reason for considering them of the same geological 
age, and which has not yet been made evident by an analysis of 
the rocks themselves, fails entirely when considered with refer- 
ence to the associa erals. 
Of the zeolites occurring on Lake Superior, =. leonhard- — 
ite and chlorastrolite appear, thus far, to be limited to a single 
circumscribed locality, while harmotome is cana in only a 
doubtful crystal. The only new zeolitic mineral noticed is 
chlorastrolite, which is quite common along the beach of Isle 
Royale, for a distance of two or three miles, - which has not 
been discovered at any other point on the 
The occurrence of the zeolites on Lake FR is not abso- 
lutely, although chiefly, confined to veins. All the fine speci- 
mens of crys stallized minerals of this class have been obtained 
from the cupriferous veins, so that this may be considered as the 
normal aes e of occurrence in this region. Where the trappean 
rocks assume an amygdaloidal structure, we have, occasionally, 
prehnite, ‘auipniakiag tel etc., in radiating fibrous masses, filling 
the cavities; but quartz in the form “= ne Beh and chalcedony 
and calcite are much more common. are occasional flat 
tabular m; masses of laumontite mixed oor shaie found lying 
in the direction of the lines of bedding of the trap, but these are 
thin and of limited extent. Many of the trap amygdules are 
filled with a mineral resembling chloropheite and others with _ 
saponite. Most of the substances thus occurring are only to be 
recog wma Wes by panies! sa as they are generally finely 
a : 
pelleted ed by Messrs, Owen and Norwood as occurring on 
nee a eck: west of Pigeon River, a region to which my ex- 
hav 
fein pr I have, however, examined numerous 
tat pat of the Lake, Take witout ving dinoverd ether of thew sen 
