o(4 7/ie ^[lini/cil II (rinhx/ist. D.MfrnlxT. IWtl 
tain iioii-oiTs ol' that t'liipiio us prodiicts of replacement of Per- 
mian and ('jirl)oniforous limestones. Another Hnssian authority, 
M. ]*. /emiatsch(Misky. entertains similar \ie\vs in respect to iron- 
ores of central Russia.* 
XV. Mithfcrriinrmi iron-onx iix n pftiri/ninfs of linn stoiwu. 
1 — Jroii-orrx iij' liillind. Spain. 
No more remarkable developments of iron-ores can Itc in- 
stanced than those of the Biscayan province of Spain. These 
ores, known far and wide undi'r <lesignations of localities of 
numerous workings on the flanks of Mt. Triano, include those of 
Somorrostro, Triano, and Matamoras. from which immediate lo- 
calities, according to Mr. (Jill, over 2^ millions of tons was pro- 
duced ill 1S82, or !»."'> per cent, of the whole i)ioduct shipped 
from the port of Bilbao durino- that year. 
These ores are of several am()ri)hous types and giadations. in- 
cluding limouites, turgitesand hematites. some of the latter verging 
upon the specular variety. They are of ditt'erent degrees of purity, 
inversely proportional to their tenor of earthy silicates; and ac- 
cording to the degree, first, of replacement of limestone, and. 
second, of alteration from the condition of ferrous carbonate, 
from which all types and gradations liave evidently l)een de- 
rived. 
These imj)ortant iron-ore deposits occupy the horizon of lime- 
stone, especially of a formation interposed between overlying 
fossiliferous argillaceous limestone, and a lower limestone under- 
hiin l)v variegated and micaceous grits, containing nodular 
sphjvrosiderite, the whole series, of Middle Cretaceous age. ])eiug 
much disrupted and dislocated. The ore. wrought in places to 
depths of over 100 feet, greatly Huctuates in thickness, owing to 
inefpiality in vertical range of replacement, whence obviously the 
uneven or billowy surface of the limestone lloor. as descrilted by 
(Jill and others. In other places the limestone is fully developed, 
no replacenuuit having been effected. Again, the whole vertical 
range of the limestone is rei)ri'seuted by ore, whik' at still other 
localities a lenticular Ijed of unaltered limestone separat«'s the so- 
called ((imjHtiii/, clearl}' a hematitic or transition product of 
alteration of siderite — more or less incompletely transformed, 
*Citerl ill Bil)l. of iron-ores. (ieol. Nat. Jlist. Surv. of Minnesota, 
Bull. No. (i, pp. 320, 3:34. 
