Geology of Lake Superior. 23 
About half-way along its north west side, from the south 
west towards the north east, parallel chains of long and nar- 
row islets of amygdaloid, containing the usual nodules, to- 
gether with native copper, commence and continue to its north 
east extremity. At the distance of about two miles further 
in the same direction is Passage Island, also of amygdaloid, 
and containing native copper in veins and cavities associated 
with prehnite, quartz and calcspar, 
In the small bays of these agmydaloidal islets, the debris 
of veins was found in great quantitics. From the rock, which 
frequently adhered to these tabular masses, it seems that 
they are from a dark brown porphyritic trap, Native copper 
in small grains, plates and wires was very plentiful in these 
masses, and was associated with prehnite, quartz and calcspar, 
These portions of a vein could not have come from far, as 
their edges and angles were notin the least worn. It is pro- 
bable, that they have been washed out of a neighbouring vein 
by the waves, 
It is.a very remarkable and interesting fact, that Doctor 
Richardson found specimens precisely similar to these, near 
the Polar Sea. He says, “* wealso found some large tabular 
“ fragments, evidently portions of a vein, consisting of prehn- 
“* ite associated with calcareous spar and native copper."’* 
This vein, (he also adds,) he supposes to be in feldspathose 
trap, 
On the south east side of Ile Royale, there are similar chains 
of islets, extending 7 or 8 milesin length, and exactly parallel 
to the long narrow point of trap sienite which is a continuation 
of the central ridge of the island, and which, projecting @ 
little beyond these chains of islets to the north eastward, 
forms the north east point of the island. Porphyry and green- 
stone are also common among these islets, and here and there 
the sundstone is visible. Further to the south west this latter 
rock 
* Appendix to Franklin’s first journey to the Polar Sea, 
