tVoui till' iiiKlcrlyiiiu- r, i,,t ,l,il,; . This is ;i soft liiuoiiitc piissiiio; 
into tiiri>itc :iii(l :ils() or:iiln:itin<:' in phiccs into ;i luu'dci- vtiricty 
known ;is r<„(i (hiru. in wliicii nliound |»s(Mi(Ionior[)lioUs riionilio- 
lu'drons of licniiititc. iiftcr sidcritc. 
Tlu' sIuUv hlnc linu'stonc. contjiinin^' /"/((/(///(^ fn rii/a/n. ;ind 
irivini>- phiec to oiv-lxxlics on the north si(h' of the (lividc bctwi'cn 
the Xorvion -Ami the Soinorrostro I'ivcrs (Mt. Trinno). presents :i 
continnons outcrop on the south side. ;ind forms the crest of tiie 
inountiiin. The rt/m duln . or ^iilierv oi'e. is desci-ilied ;is the 
chnnicter of oi'e deep under cover: iiinijxiiill. tlie ciioice or >hip- 
pin;j; ore of the re^'ion. umh-r moderate cover: :in<l ml, in. w 
worthless xarietv in e\|»osed ledo(>s. The latter is a sidi-ritic. 
cellular, cherty limoniti', foi'minu' outliers or crairs. evidently coi- 
resi)ou(lin<>: to the upper ed<2;e of disruptetl and highly tiite(I 
masses of tiie fi(jini uin limestone, weathered and leaclie<l liy at- 
mospheric action without the aid of undertrround moisture, and 
without protection of co\(m-, l)Ut })assin<r into rciin on attainiiiu' 
cover. In both l)rown and red-ore mim>s sidei-ite occurs in l)locks 
as cores or nuclei of altered i)roducts. 
The source of ferrous salts yieldinu- more or less alh^ralile fer- 
rous carbonate in contact with limestone, appears to have lieen 
overlying, now mostly ol)literated, ferrifer<)us and pyiit<)us sedi- 
ments, of which remnants are preserved. I'neqnal conditions, 
])ei'lia[)s in original composition of the oi'c limestone. l>ut cei-- 
tainly as to attitude and environment, have led to une(|ual ile- 
velopment of ore-masses, some of which, according to (lill. hav- 
ing the semblance of mountains of ore, proving iiieic shells of 
good ore with nothing but siliceous matei'ial liehind them. 
(.'luuiges of volume, as uneiiual replacement and chemical altera- 
tion have advanced, may l»e believed to have been adc(|ii;itc to 
pi-oduce no small part. if not thewhole. of the (lisrupt ions and dis- 
lo(!ations, so marked a feature in the stratigraphy of the icgion. 
Though some of the phenomena heic icferreil to liaxc lieen 
ditl'erently interpreted by >[. liarson" ami .Nj. Uaills.t tiie descrip- 
tions given by (JillJ furnish al)undant evidence of sideritic replace- 
ment of Cretaceous limestone strata, and of sul)si'(|uent altei'a- 
tion into limonite and hematite more or less advanced as condi- 
*Kev. luiv. (Ifs Mines, iv. 187s, (;4S. 
tAiiiKilps .les Mines. \v. IsUt. •,>(i!(. 
J.I our. Irtii) and Steel Inst. \>^^-l, iV-). 
