120 NEW YORK STATE MUSEUM 
The deposit is of petrographic interest as it differs from the 
others already described in certain details; the magnetite is, in com- 
mon with all the deposits, of very late magmatic stage, but instead 
of replacing Pochuck-Grenville the magnetite of this particular belt 
is closely related to its allied igneous member, the Pochuck syenite, 
and occurs as an end-emanation product in it and actually in part 
replaces some of the minerals of that rock; the “ pneumotectic” pro- 
cess of Graton and McLaughlin,*®® but a process which the writer 
prefers to think of as deuteric.**? 
The properties have not been worked to any great depth, and 
there is no doubt but that much magnetite remains in the mines 
which might yield good ore to modern magnetic concentrating 
methods. 
The Clover Hill mine. This mine is situated on the extreme 
southwestern end of what is presumably an extension of the Brew- 
ster belt, a little southwest of the village of Croton Falls in West- 
chester county, on the Butler property. There is said to have been 
a magnetic concentrator in operation on this property at one time, 
but the writer has no definite knowledge of it. The workings con- 
sist of open cuts; the ruins of a tramway lead to an old foundation 
(on which a dwelling has been erected), originally a foundation for 
one of the mine houses. The cut, which had been sunk through a 
cover of drift, was full of water at the time of the writer’s visit. 
In the vicinity of the cut a zone of strong magnetic attraction 
nearly 100 feet wide may be traced by means of a dip needle across 
the strike of the ore body; since the ore lies in the same line of 
strike as the Croton magnetic mines, and since it shows the same 
general petrographic behavior and association, it is probable that 
it properly belongs to the same belt, and that it has the same origin. 
The walls of the cut are essentially granite, however, rather than 
syenite ; the rock consists of oligoclase, microcline, orthoclase, quartz, 
with both pyrite and pyrrhotite. The walls have a decided gneissoid 
structure, the streaky habit being in part due to bands of magnetite ; 
the ore apparently grades into the wall rock in a manner precisely 
similar to the ore in the Croton magnetic mines. 
Considerable shearing is in evidence, and a crush-zone dipping at 
a low angle cuts the rock at the south end of the pit, so it is certain 
that the ore body has been more or less disturbed by deformation. 
168 Graton, L. C. & McLaughlin, D. H. Further Remarks on the Ores of 
Engels, California. Econ. Geol. 13: 81-99. 1918. 
169 Sederholm, J. J. Synantetic Minerals and Related Phenomena; Bull. 
de la Comm. geologique de Finlande No. 48, p. 141-42. 
