and its associates on Lake Superior. 245 
4. Datolite; compact amorphous, white translucent mass, 
covering the prehnite with a layer of which # inch thickness, 
still remains. The copper threads do not penetrate it. 
o. 138. PEwABIC COPPER-BEARING BED.—This specimen— 
about 24 inches by 84 by $—is evidently from the interior of a 
druse, to whose wall it was attached by only a small part of its 
surface. The body of the specimen is copper, very cavernous, 
much of it pseudomorphous after laumontite. The copper is 
very thickly bestrewn with small green crystals of quartza— 
prisms terminated at both ends,—which are however older than 
the copper. On the sides and around the edges of the speci- 
men there are beautifully modified scalenohedrons of calcite. 
The successions are: 
. The rock or mineral to which the laumontite was originally 
attached, and which has disappeared. 
: aumontite or leonhardite; has also disappeared ; the 
— were } to 4 inch long, terminated at one end with a hemi- 
ome, 
mineral ; laumontite crystals occur frequently enveloped, except 
the base, in calcite 
4. 
both ends. They occur on parts of nearly every one of the 
ported only by the copper which is younger. 
The asiisin do petels couihla minute, brilliant particles of eop- 
pe oe in describing other specimens. 
ical forms, with radiating structure, scattered over the quartz 
