192 G. H. Williams—Norites of the “ Cortlandt Series.” 
The writer has already described another rock from this sec- 
tion® (a peridotite, No. 54), occurring in the bed marked by 
Professor Dana “a,” as showing in a marked degree the effects 
of pressure, while No. 48, from his band “/” is still more re- 
markable in this respect. This rock was once a gabbro, like 
that to be described in the sequel as occurring at Munger’s 
Corners (No. 42). At present it is highly altered both struc- 
- turally and mineralogically. The diallage is largely changed 
to hornblende and is drawn out into long lenticular patches. 
The feldspar is mostly broken up into a mosaic which bends 
‘around the pyroxene, producing a fine gneissic structure. In 
fact this rock is almost identical with some of the more altered 
“Flaser gabbros”’ of Saxony, which Professor Lehmannt has 
so conclusively shown to have resulted from the action of pres- 
sure upon massive rocks. 
The hornblende norites (Nos. 50a and 500) from this sec- 
tion mentioned above are wholly massive and show no internal 
evidence of having been subjected to pressure. 
A careful study of the rocks of this interesting section, both 
in the field and with the microscope, has convinced the writer 
that they offer an unusually plain and instructive instance of 
the metamorphism of eruptive rocks by pressure. The evidence of 
bedding, seen in the cleavage and parallel arrangement of the 
constituents, instead of being an indication of original sedimen- 
tation, ws a secondary feature. ‘The action of the pressure was 
here so slight that original structure is not wholly changed, as 
is more usually the case; but the alteration has only taken 
place along certain planes which allow the tracing of transitions 
into the original, unaltered and still prevailing form of the 
rock. 
No, 6a from near Cruger’s Station, is a remarkable variety 
of mica-norite, in which the hypersthene is segregated into 
irregular patches. Outside of these the rock is a typical mica- 
diorite composed of plagioclase, biotite, magnetite and apatite, 
together with ‘a considerable amount of garnet which is a sec- 
ondary crystallization. Within the segregated areas the space 
is almost wholly occupied by hypersthene, which exhibits in a 
striking manner its alteration to secondary fibrous hornblende. 
4, Augite Norite or Hyperite. 
Professor Dana has communicated the following analyses, by 
Mr. M. D. Munn, of a specimen of augite-bearing norite from 
the northern part of Montrose Point on the Hudson River.t 
* This Journal, Jan., 1886, xxxi, p. 39. 7 lb @y [Ds LOO: 
t This Journal, Aug., 1881, xxxii, p. 104. 
