370 The Ahu't'ican Geohujisf. Deoembor, isai 
the lamented Prof. 11, ]). Irxinji. and later by ^ll■. ]). 11. Browne. 
ami hy Mr. C. K. ^'an llise.* 
The eonelusioMs of the })resent memoir seem, as may be 
elaimed. to strengthen the prol)abiUly that occurrences of siderite 
and ferro-calcite. like those described by these authors as the im- 
mediate source of hematite in the I*enokee-Gogebic range of Wis- 
consin and Michigan, are of the nature of chemical replacements 
of limestone, and calcareous shales and grits more or less car- 
bonaceous. Such developments are dou)>tless remnants of sider- 
itic material, of which the greater part has l)een further altered 
into brown and red hematite successively. 
As indicated by these writers themsidves. from soluticjus of 
ferrous salts, replacement of calcareous material has lieen effected 
according to local conditions determining circulation and inter- 
ception of these infiltrations. That this was once, or at least in 
part, direct, is shown In' the development of siderite. J*roducts 
of indirect n-placement like ferric oxide proceed as in other in- 
stances either from spontaneous oxidation (jf the replacing carbon- 
ate, or from its tardy alteration. The i)art taken by dj'kes in the 
interception of drainage has i)articularly been shown by A'an Hise. 
Replacement of limestone by siderite, and sul)se(pient altera- 
tion of this epigene product are opposite phenomena incidental to 
essentially ditferent atmospheric environment. Carbonic anhy- 
dride, or reducing gases, or a mixture of l)oth. which may be 
assumed to have prevailed concurrently with the first process, or 
rather wherever this was set up. eventually must have given waj' 
to an ordinary oxidizing atmosphere. The association of car- 
bonaceous strata sufficiently attests this p<jint. 
FoKKlCN K.X.VMIT.K.'^ OK RKPLACKMKNT OF LIMKSTONK UV 
IRON-ORKS. 
T close the present memoir with a few brief illustrations of re- 
l^lacement <^>f limestone by iron-ores in well known and important 
developments in several parts of Kuroi)e. As such most of these 
have l»een distinctly recognizeil. 
IX. Jiiphnt iiiciif tif CurhoiiiftirouK. limrstoiic. Eiiyhni<L 
The Carboniferous or Mountain-limestone series of the north- 
ern and north-midland counties of England, as in other parts of 
that island — especially in South Wales. consists of alternations of 
=*=.\m. Jour. Sc. .\xxii, I88li, '^r).!; xxxvii, 1889, 82, 299. 
