Geology and Mineralogy. 407 
netic state of the iron is in some places due to secondary causes; 
i. e. the heat of intrusive rocks erupted since the iron ore and jas- 
r were in pl While in general the Republic Mountain ore 
Is hematite, exceptions exist. On the northerly side of the hill a 
“diorite” dike was seen, It is found that the ore was so affected 
by the heat of this intrusive mass that it is magnetic adjacent to 
it, while a short distance away it is the normal hematite. 
Numerous oth examined about the hill where 
these secondary intrusions occurred, with the same result; the iron 
ore was ma ¢ adj he dikes, but gn hort 
dista 8 neral rule, the magnetite or the hematite 
pseudomorphs after it (martite) are found near the “ quartzite” of 
Brooks mine. Those who examine the map of Republic 
Mountain, hc ed by him,* will observe on the northern side ot 
his “ quarz ” a queer tongue of it heat into the hematite. 
An ioe. of this tongue at different places shows the fol- 
while the centre of the mass is free from them. At this point it 
varies from a few inches to two feet in width, and it is seen ” 
break across the lamination, although nearly ee with i 
At another part shown near the same pit, this rock pe 
its contact with the “jasper” and ore were well marked. The 
‘quartzite it _is firmly races a a e, and breaks oe the 
din 
ore, e Faneten is an eee (intrusive) ae and not 
one sediment w 
another. The ore at the junction is magnetic. The question 
whether this is an intrusive or sedimentary rock has another side 
than the simple scientific one. It makes a great difference in the 
mine whether this is a Rae Se ovarlyius metamorphosed sandstone, 
as Mr. Brooks Moet it, ora later intrusion cutting the ore be low. 
This latter case opens numerous aieane that the practical 
man can only discret to his cost, sooner or later, but whic 
have nothing to do with the present discs sion. 
this rock seems to belong to the granites, it will be 
described under them. Should future pee cig show that all of 
the “quartzite” of Republic is the same as the tongue is, it 
would have a bearing on the proximity of the magnetite and mar- 
tite to it Me 
re pr 
nent feature. It seems, so far as we have a that the magne- 
tite and martite are directly proportioned to the amount and 
proximity of eruptive a8 extravasated ee the ore was in 
* Atlas, Geol. of ele 1869-73, Plate VI. 
