MAGNETITE IRON DEPOSITS OF SOUTHEASTERN NEW YORK II5 
the titanium exists in all of the ore bodies described. The quantity 
of titanium oxide in a sample of ore selected at random, at the mine, 
was determined by Prof. H. T. Beans of Columbia University, who 
found in the sample of ore submitted, 1.01 per cent Ti02?. 
The ore, a coarsely crystalline magnetite, carries remnants of still 
unreplaced rock, with sericitization as a just preceding and accom- 
panying feature of the magmatic end-stage replacement process 
(mineralization by deuteric process). ‘These features are illustrated 
in plate 6, figures 2 and 3, which exhibit both deuterization of the 
feldspar, sericitization and replacement, and in plate 7, figure 2. 
The ore grades into the wall rock, passing from solid magnetite, 
through lean ore, to essentially magnetite-free wall rock (Pochuck- 
Grenville). 
The evidences of deformation are so pronounced that very care- 
ful exploratory work should be undertaken in order to locate the 
existing faults and prove the presence of a sufficiently large body 
of magnetite to be profitably mined. 
The Sprout Brook belt. Sprout Brook valley is a narrow, long, 
moderately deep trench cut into a belt of crystalline limestone; the 
limestone may be regarded as one of the few examples of unmixed 
Grenville exposed in the area under discussion. Sprout brook is 
essentially an extension of Canopus creek, which lies to the north- 
east, and which flows into Sprout brook. 
On the eastward-facing slopes of the ridge of gneiss which forms 
the western margin of the valley, are located the Croft and the Todd 
mines; one, the Croft, is on the northern end of the belt, the other, 
the Todd, is on the scuthern end in Westchester county, on the estate 
of Mr Stuyvesant Fish. 
The two mines are approximately 3 miles apart. Both mines 
were rather extensively worked some 30 or 40 years ago; a very 
good description of them during their active operation is contained 
in Putnam’s*’* report, which is illustrated with maps and diagrams. 
The Todd mine was owned and operated by the Fallkill Iron Com- 
pany, which shipped the ore to Peekskill on a narrow-gauge rail- | 
road, and thence by boat to Poughkeepsie where its furnaces were 
located. During the census year (1880), 4032 tons of ore were, 
mined. According to Putnam (op. cit.) the east wall of the main 
pit was composed of crystalline limestone, and the ore body was 
from 3 to 4 feet wide. Whe ore carried 44.34 per cent iron and 
0.033 per cent phosphorus, with admixed calcite and pyrrhotite, 
158 Putnam, B. T. Tenth Census Report, 1880. 
