OKIGIN m IGNEOUS ROCKS. 98 
L>olng from one pocket to another along the strike there is often notli- 
ing- to indicate the vein but a small seam of chlorite. The pockets are 
:ilmost continuous in the direction of the so-called dip and hold this 
iip very constantly. 
It seems to me that this j^ortion of the amphibolite band was an 
igneous mass intruded after the formation of the sericitic schists, and 
^•ither after or at the time when these scdnsts Avere ah'eady tilted to 
Iheir present ])osition, and that the emery bed is the result of the dif- 
ferentiation of components of the mass that were held in solution by 
Ihe igneous magma. 
The theory that Professor Emerson " ])roposes is also ])robable, viz: 
That the emery-magnetite vein was originally a deposit of limonite wliich was 
formed by the replacement of limestone and into which alumina was carried by 
nfiltrating solutions and deposited as allophane and gil)bsite. The subsequent 
betamorphism of the bed, although it may well have been intimately connected 
ivith 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 
>hown by the jointing and brecciation of the magnetite and emery. * * =■= 
["he less altered ferruginous limestone below was changed into the epidoti(r 
jmphibolite. 
Many points that can be noticed support this conclusion, but these 
dso indicate an igneous origin for the amphibolite. No fresh per- 
dotite rocks have been observed in this section, and the nearest are 
probably across the Connecticut River at Pelham, where an igneous 
nass of saxonite occurs. However, as stated above, the presence of 
;hromite in the serpentine associated with this amphibolite seems 
^ood evidence that the serpentines have an igneous origin, and it 
s very probable that they are alterations of former masses of an 
ntruded peridotite. 
If any deep mining is undertaken on the emery, new evidence may 
)e broufifht to liijht that will determine decidedly what nuiv have been 
he origin of these amphibolites and emery deposits. 
ORIGIN OF CORUNDUM IN NORITE. 
The emery variety of corundum, which is found associated with 
he norites in the vicinity of Peekskill, Westchester County, N. Y., 
hows a gradual transition of the spinel (pleonaste), iron ore, and 
niery into the normal norite. It is not at all unlikely that the 
egregated masses of these basic minerals are the products of dif- 
erentiation of the molten norite magma by which the basic portion 
>f the magma has been ccmcentrated near its outer surface and makes 
L gradual transition toward the center to the more acid norite. 
riiis occurrence would be similar to that of the pyrrhotites which 
lave separated out from the norites of Nor\vay, as described by 
Mon. U. S. Geol. Survey, vol. 20, 1898, p. 145. 
