and its associates on Lake Superior. 247 
The pseudomorphs of copper after laumontite are prisms } to 4 
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angles are often sharp, though in some instances the j 
two faces of a prism presents something of the appearance of a 
copper cast made in a mould whose two halves fit only imper- 
fectly together. Sometimes, under a strong glass, the joining is 
clearly imperfect, and the pseudomorph has the effect of a prism 
built with four badly-soldered plates of metal. atlas 
Minute prisms of quartz (colored green by the chlorite-like 
mineral mentioned in specimens No. 13 and 14) project from 
the interior of the pseudomorphs, through the copper, to 735 of 
an inch above the surface. ; j 
In one place I cut to the depth of ;', of an inch in solid cop- 
per; but a cross fracture in another prism showed that the 
copper was, there, a mere superficial film, while the.interior was 
u porous mass of quartz 
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often perforated with holes, but it often shows flakes of copper 
Nising on edge to a height of yz of an inch above the face. 
marked signs of change to datolite. The transparent crys 
pearly lustre on the cleavage 
Planes, and a little farther away this mba a Pai ss 
insensibly into a lustreless white mass composed of an 5a 
tion of exceedingly minute crystals, which exhibit the d lite 
form under the microscope, and fuse easily with the characteris- 
tic green flame before the blowpipe. The same change Had 
Visible, in places, on the fees 5 of calcite enveloping t 
Pseudomorphs after laumontite. 7 
The relative ages here appear to be, 1, The amygda F% 
though probably not in its present condition ; 2, Laumon rg 
3, Quartz; 4, Copper, chlorite-like mineral; 5, Calcite; 6, Datolu 
