1893. | NEW YORK ACADEMY OF SCIENCES. 91 
conclusion has usually been drawn that they have been derived 
from blende and pyrite, by oxidation. If this ever were the 
case in the ore bodies here considered, oxidation must have been 
extraordinarily thorough, before the period of metamorphism, 
for blende and pyrite are both extremely rare minerals in the 
mines and do not oecur with the ore proper, but with the 
horses of silicates. If, however, such an oxidized mass of 
limonite, smithsonite and calamine had been present, metamor- 
phism could much more readily bring about the chemical com- 
pounds that we find to-day. We cannot readily conceive of 
metamorphism changing the sulphides directly to the present 
minerals. The absence of the sulphides increases the difficulty. 
4. Although the ore is in a disturbed region, no faults have 
been met in the mines which might serve as a source of the 
original ore bearing solutions, nor do any fissures cross them so 
far as known. There is no evidence to show that the ores them- 
selves have filled a fissure parallel with the bedding, although it 
is possible that they may have been directed by one, or better 
yet by a set of bedding planes and spreading thence have re- 
placed the walls. But as they are in a narrow belt of rock, 
which probably is,as Mr. Nason strongly argues, blue Cambrian 
limestone, locally altered by granite intrusions, I think the 
causes cited under 5, have greater weight, than main supply 
fissures. ' 
5. If we do not admit, and indeed it seems unreasonable to 
me to do so, that the bodies of iron-zinc-manganese compounds 
have been deposited along with the limestone and at a certain 
stage in its growth, there is but one stimulating cause for ore 
solutions left, and that is the intrusive rocks, already referred 
to. While this cause cannot be demonstrated to be without ques- 
tion the true one, these dikes and intrusions might have natur- 
ally started circulations, which, spreading from their contacts 
with the limestone, along a favorable bed, surcharged the lime- 
stone with the ores and attendant minerals. In just what form 
they were originally precipitated we cannot well say, although 
as stated general experience the world over would suggest sul- 
phides. It is possible as Mr. Nason suggests (N. J. Rep. 1890, 
p. 47-49) that the sulphides with the magnetite at Andover and 
Oxford Furnace to the south represent such originals in a less 
altered form. If they were originally sulphides, they were 
doubtless oxidized by atmospheric agents, to the usual secon- 
dary minerals, and then metamorphosed. 
6. The small bodies of magnetite along the contact of the 
limestones with granite, and the larger manganiferous one under 
the fold of the zinc ore at Franklin (see New Jersey Report, 
