AO Captain Bayfield oa the 
Privusico.—In amygdaloid, Point Mamainse. ( Bigsby.) 
Cray Iron Stone.—In a vein = an inch thick in amygdaloid, 
Point Mamainse. ( Bigsby.) 
Tron Pynites,—Was found in various parts of the north 
coasts Disseminated in cubic crystals 
through greenstone slate—slate islands ; ia 
granite—Neepigon Bay. Lastly, in very 
considerable quantities, both massive and 
crystallized, in slate subordinate to the old 
red sandstone, on an islet betweeu Wedge 
Island and the main land—eastern part of 
‘Neepigon Bay. At this place it was also 
found in veins traversing the black slate in 
the most beautiful manner in all directions, 
ahd having imbedded crystals of quartz, 
fluor, and calcspar. 
26. Iron is a very abundant material in the trap rocks of 
Lake Superior, rendering them more or Jess magnetic. They 
always disturb the magnetic needle, and, in many places, so 
strongly as to change the variation two points, In one place, 
the eastern entrance of Black Bay, this local attraction was 
so great as to render the compasses useless, the North re- 
maining in any direction or point of the horizon to which it 
might happen to be placed. Whenever the theodolite was set 
upon a granite or sandstone point, the needle remained un- 
disturbed. On a trap point it was always the contrary. 
When we were running lines in the boats from a granite 
headland to one of trap rocks, we could frequently plainly ob- 
serve the direction indicated by the compass on the boat’s 
table to change, in some cases, a point or two as we ap- 
proached the latter, and resume its former correct direction 
as we returned, or as we proceeded ont into the lake, without 
the sphere of its influence, 
ie 
