200 GEOLOGY, 
masses, or concentric layers of the same or other minerals. A good illustration of this structure 
was carefully copied, and is represented of the natural size in the figure. 
4 ¬ Epid 
>... Garnet and quartz. 
--. Hornblende and quartz. 
Quartz. 
一 Hornblende and quartz. 
-~ Quartz, hornblende, mica, and feldspar. 
SEGREGATION IN GRANITE. 
The central portions of the mass were of epidote of a light green color, without any distinct 
traces of crystallization. This was surrounded by a layer of garnet, intermingled with a small 
portion of quartz and feldspar ; next a layer of hornblende and quartz in fine grains, the outer 
part being more quartzose ; then a layer of the same minerals in a state of more perfect lamina- 
tion; and, lasily, the same in a more coarsely crystalline condition, containing a portion of 
mica. This alternation of minerals in various conditions of arrangement is repeated indefi- . 
nitely, and an instance of a much more complex character might have been selected—one in. 
which a greater number of lines of minerals could have been represented. 
These peculiarities of structure are similar to those seen in the granitic and metamorphic 
rocks of the Appalachians and in the azoic rocks of northern New York, where magnetic iron 
frequently forms the centre of the nodular masses. By the extension or drawing out of such 
lenticular aggregations the lines of minerals become nearly parallel, and numerous examples of 
this were observed. We must look for an explanation of these phenomena to the action of 
forces of crystallization, or polarity, when the rock was in a semi-Auid state; the stratiform 
condition which results should not be regarded as proof of a sedimentary origin of the rock. 
The rock under consideration is very probably a metamorphosed sediment, but the linear 
arrangement of the minerals is not regarded as a satisfactory evidence of it. The structure 
also appears to have taken place in the rock when it was so far fused as to obliterate the original 
planes of stratification, if any existed. I therefore avoid the use of the words strata or stratifi- 
cation in relation to these rocks, and designate the lines or layers of minerals as planes of 
structure, or of lamination. "These planes, as developed in the granite ridge that has been 
described, have a direction or trend nearly north and south; there are, however, several local 
variations of 10° to 20° from this direction. Their dip is westward, at an angle of 75°, which 
was found to vary at different points of observation. ۱ 
The rocks are cut and traversed by several granite and quartz veins running in various 
directions transverse to the planes of structure. One narrow vein, composed principally ۷ 
سح‎ feldspar, was observed to conform to the direction of the lamination a 
-C | part of its course, and then to pass diagonally for a short distance, cutting 
E = across the planes of structure, and “ faulting” a narrow seam of quartz as 
if it had been forcibly inrupted. The walls of this vein consist of feld- 
spar, mica, and hornblende; the junction between them and the vem 
ichs appears to be perfect, and does not present any indication of fracture. 
In one of the small cafions of the ridge, a vein of ferruginous quartz about two feet thick 18 
