Secondary Occurrences of Magnetite. — Kimball. 13 
ing to it), though it is only north and west from Scotland 
that that face stands out in bold relief above the country to 
the south. Around the western end of the fold the southern 
mountain escarpment turns irregularly to the southwest to 
White Oak mountain in Pope county which mountain owes 
its elevation to the Red river monocline. 
The sudden turn of Middle fork at Settlement postofflce 
is due to this fold as is also the northeast course of Weaver 
creek west of Settlement postofflce, and the course of South 
fork of Red river from Scotland to Clinton. 
In the neighborhood of Scotland and west of that place 
there are several more or less prominent ridges made by the 
tilted sandstones at the south side of the fold. Here there is 
also a small syncline of which these ridges with the south dip- 
ping beds form the nortjh side (see fig. '6). 
SECONDARY OCCURRENCES OF MAGNETITE ON 
ISLANDS OF BRITISH COLUMBIA BY RE- 
PLACEMENT OF LIMESTONE AND BY 
WEATHERING OF ERUPTIVES. 
By James P. Kimball, New York. 
(Plates II and III.) 
The present paper is designed as a continuation of publi- 
cations in the year 1891.* The occurrences here referred to 
clearly conform to two separate types of ferriferous deposits 
which it has seemed important to distinguish as hydro-chem- 
ical replacements. As previously described, one type is a 
morpiiological replacement of limestone by double decompo- 
sition between ferrous salts and calcic carbonate, the former 
being generated from ferrous silicates; the other type, a par- 
tial, and not necessarily pseudomorphic, replacement of ferrous 
silicates in weathered basic rocks, or as more explicith' dis- 
tinguished, a residual concentration or fixation of iron oxides 
incidental to development of soluble alkaline carbonates from 
weathering oxidation or splitting up of ferriferous silicates. In 
replacements of limestone ferriferous material is generally de- 
rived from extraneous though c()ntiguous sources through 
simple permutations and reactions which I have elsewhere 
followed out. 
*Am. Jour. Sci., xLii, 231: Am. Geologist, viii, 352. 
