26 CORUNDUM IN THE UNITED STATES. [bull. L80. 
then, would indicate the existence of former masses of a basic mag- 
nesian rock which have been changed into serpentine, the serpentini- 
zation continuing into the amphibolite for some distance. 
The emery is not continuous along the strike of the vein, but occurs 
in a series of pockets in the vein that dip about 80° to the north. In 
going from one pocket to another along the strike there is often noth- 
ing to indicate the vein but a small seam of chlorite. The pockets are 
almost continuous in the direction of the so-called dip and hold this 
dip very constantly. 
It seems to me that this portion of the amphibolite band was an 
igneous mass intruded after the formation of the sericitic schists, 
and either after or at the time these schists were tilted to their pres- 
ent position, and that the emery bed is the result of the differentia- 
tion of components of the mass that were held in solution by the 
igneous magma. 
The theory that Professor Emerson 1 proposes is also probable, viz: 
That the emery-magnetite vein was originally a deposit of limonite which was 
formed by the replacement of limestone and into when alumina was carried by 
infiltrating solutions and deposited as allophane and gihbsite. The subsequent 
metamorphism of the bed. although it may well have been intimately connected 
with the extremely violent mechanical forces to which the strata have been sub- 
jected, was largely completed before these forces had ceased their activity, as is 
shown by the jointing and brecciation of the magnetite and emery. * * * 
The less altered ferruginous iimestone below was changed into the epidotic 
amphibolite. 
Many points that can be noticed support this conclusion, but these 
also indicate an igneous origin for the amphibolite. No fresh per- 
idotite rocks have been observed in this section, and the nearest are 
probably across the Connecticut River at Pelham, where an igneous 
mass of saxonite is encountered. The presence, however, of chromite 
in the serpentine associated with this amphibolite is to me very good 
evidence for believing that the serpentines have an igneous origin, 
and it. is very probable that they are alterations of former masses of 
an intruded peridotite. 
If any deep mining is undertaken on the emery, new evidence may 
be brought to light that will determine decidedly what may have been 
the origin of these amphibolites and emeiy deposits. 
CORUNDUM IN NORITE. 
In the vicinity of Peekskill, Westchester County, N. Y., corundum 
has been found associated with norites, which have been described 
by G. II. Williams. 2 These rocks belong to the Cortland series, of 
which the prevailing rock type is one that is characterized by the 
presence of the mineral hypersthene. But though this mineral is 
i Mon. U. S. Geol. Survey Vol. XXIX. p. 145. 
'•'Am. Jour. Sci., 3d series, Vol. XXXIII. 1887, pp. 135, 191. 
