and its associates on Lake Supervor. 257 
swimming, if one may use the word, in the interior of the crys- 
tals; and these are ‘so disposed as to lead to the idea that 
ee hans the growth of the younger crystals they had to con- 
re : e 
IIL —The copper has entered the calcite crystal since its growth was 
Jinished. 
A specimen, in my collection, illustrates this remarkably well. 
It 18 a cleavage-rhombohedron of opaque calcite, traversed b 
intersecting sheets of copper, which are wholly independent of 
‘ous sheets of copper =, to z's inch thick, which are per- 
fectly straight. These sheets are parallel to several i 
Sets intersect each other, the resulting solid one composed of 
of the specimen the copper predominated over the calcite. 
erever Wie taoes of the ai laminz are exposed, they are 
marked with a delicate, reticulated tracery, indicating the lines 
of intersection of the sheet with the cleavage planes of the 
crystal. The cement in the vicinity of the calcite is resid 
hated with copper; in places it is almost wholly replaced by . 
‘netal in the fine granular condition called ‘‘ brick copper, i 
into this the laminews of metal extend, without break, from the 
— This specimen is really a pseudomorph of copper after 
icite, 
Copper and Silver-—It is a well known fact that these two 
metals occur in the metallic state, in the Lake Superior depos- 
