aN i a eh 
PTT OT OL ee ee ee 
of the Specular Iron-Ores of Santiago de Ouba. 427 
from which, however, they are readily distinguished by their 
superior hardness and density, and by their sharp metallic sound 
when struck with a hammer, as well as by the circumstances 
of their metasomatic association with unaltered or incompletely 
altered dioryte. 
What has determined the localization of such deposits within 
the dioryte mantle has not been made clear. Certain indicate 
circumstances rather than well ascertained facts, seem to bear 
upon this question. (1) The location of such deposits, as far 
as recognized, is near the contact, but not uniformly immedi- 
ately back of it, as in the case of the ore-bodies of coralline 
parentage. Some relation between the two classes of deposits 
may be suspected from the fact that an occurrence of this 
kind is recognized alongside, and probably in contact with, the 
developed lenticular north ore-body of West Mine Hill; while 
alongside a similar trappean concentration in Dry Arroyo, 
further up the same hill, the presence of lenticular ore-bodies 
of the nature of replacements is indicated. 
Ferriferous parts of the dioryte referred to are usually 
and its bleached and obviously weathered products. Such 
occurrences are a conspicuous feature of the first range of foot- 
hills. On the Yuca Mine location, what appears to be garnet- 
iferous casts of corallum have been found in juxtaposition with 
an ore-deposit of this description. This is the only relic, if — 
such it be, of the former existence of corallines discovered by 
me so far back as this range of foot-hills. 
€ question therefore arises whether obscure and in some 
places obliterated corallines may not under such circumstances 
ave given way to available replacements of which ferric oxide 
was but a minor part, and have determined the loci of ct 
oe ap 
SA ible eruptive, followed by concentration of ferric oxide. 
he peroxidation of ferrous oxide 2n situ is easily conceived to 
have been a result from the tardy circulation, in so dense an 
Aggregate, of chalybeate, or of solutions of the vitriolized pro- 
ucts of iron and copper pyrites, especially under the further 
Condition of an adjoining body of limestone. Calcie carbonate 
4s also been at hand from decomposing silicates. 
As a corroboration of the general induction, such occurren- 
€es may be held to attest an originally more basic constitution 
of the dioryte, and especially a once larger 9 see of 
ferrous oxide, and accordingly of proto-silicates. M e 
bitions of the same general class, but clearly without the 
mediation of limestone, are outcropping surfaces of diorytic 
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