OT ME EE nL , 
J. D. Dana on Serpentine Pseudomorphs, ete. 371 
with the various harmonies of cosmical and molecular mass and 
motion which I have published elsewhere ; facts which seem to 
me to lend new probability, if not moral certainty, to the belief 
in a discoverable and measurable uniform origin of all physical 
Philadelphia, August, 1874. 
Art. XXXIV.—On Serpentine Pseudomorphs, and other kinds, 
Jrom the Tilly Foster Iron Mine, Putnam Co., New York; by 
James D. Dana. With plates VI and VIL 
Tue “Tilly Foster” iron mine is situated about two miles 
and a half to the northwest of Brewster, on the Harlem Rail- 
road. The rocks of the region are Archean, being part of the 
Highland Range, which reaches from New Jersey, across East- 
ern New York, nearly to the borders of Connecticut. The ore 
of the mine—magnetite—-is distributed, according to a pub- 
lished report, through a band 182 feet wide; and, like that of 
Northern New York and other Archean regions, it constitutes 
a bed conformable to the stratification. 
he special mineralogical interest of the locality was first 
ascertained by Professor O. D. Allen. of the Sheffield Scientific 
School of Yale College, and the collections made by him haye 
been the source of many of the facts which are here detailed. 
Prof. Allen has given me further aid in the research by his 
chemical examinations Prof. Brush too has kindly placed 
the specimens in his cabinet before me for study. I have also 
visited the region. and thus added to the number and variety of 
the specimens under examination. The analyses and descrip- 
tions of some of the minerals of the mine by Mr. E. S. Breiden- 
baugh, in a paper published, in 1873, in the sixth volume of 
this Journal (p. 207), have given me additional assistance. 
L GEOLOGICAL STRUCTURE OF THE REGION. 
‘1. Archean rocks.—The Archean rocks of the region are 
mostly different varieties of syenyte and syenytic gneiss, from 
black to white in color, and, as usual in Archean formations, 
they are often in abrupt alternations, so as to make broad bands, 
riband-like, of black and white, with black blotchings; and 
the lines of bedding are much contorted. The syenytic gneiss 
varies to a granular hornblende rock, containing little feldspar ; 
also to a whitish granulyte-like rock, but little schistose, con- 
sisting of quartz and orthoclase, with a very sparse sprinkling 
of hornblende; also to a hornblendic gneiss, in which both 
hornblende and biotite (or a black mica) are present: also to a. 
