20-4 
GEOLOGY. 
portions of the rock the crystallization of the hornblende is fibrous and acicular, resembling 
varieties of asbestiform actinolite. This rock, for a thickness of twenty feet, is entirely free 
from either quartz or feldspar ; and, like all aggregations of fibrous hornblende, is very tough 
and difficult to break. 
From this point to station 172 the rock is a syenitic granite, showing a structural arrange¬ 
ment of the minerals, and changing by insensible gradations to varying conditions of lamina¬ 
tion. Hornhlendic, micaceous, and chloritic slates, with imbedded quartz, succeed. 
At station 176 there is an exposure of a peculiar quartzose rock, forming a bed, in which the 
quartz is disposed in nearly verlical planes, interleaved with delicate films of brilliant, silvery 
mica, which fold around the grains of quartz on the flat surfaces, and disguise the true char¬ 
acter of the rock, which can only he seen in a cross fracture. 
East of this laminated quartz rock there is a succession of chlorite rocks, with a slaty struc¬ 
ture, and much stained by oxide of iron. At 183, a series of outcrops of quartz rock and white 
crystalline limestone commences. The beds are of various thicknesses, dipping to the east, or 
southeast. The quartz rock, which is the first of the series, and adjoins the ferruginous chlo¬ 
ritic rock, is compact, amorphous, or sub-granular, and is without the usual vitreous lustre of 
quartz. Portions of the rock are deeply stained with oxide of iron, probably from the infiltra¬ 
tion of ferruginous water derived from the decomposition of pyrites. There are also indications 
of structure or stratification in the mass. Its general appearance and condition is entirely 
different from that of the granitic series that has been described, and it resembles a sandstone 
in a condition of semi-metamorphism. The white limestone is in immediate contact with this 
quartz rock. Its texture varies from the ordinary coarsely crystalline varieties to a compact 
sacharoidal marble. Scales of graphite are disseminated in some portions, hut no other mine¬ 
rals commonly occurring in such limestone were found at this outcrop. The width of this bed 
was about 200 feet, and it was succeeded by another similar one, separation between them being 
effected by a thin bed of quartz rock, conformable with the limestone beds, and similar to that 
last described. 
The relations of the series can be seen on the section, or in the annexed section from the note¬ 
book, in which, however, the relative thicknesses are not correctly represented. 
LOCAL SECTION NEAR STATION 183. 
& b c b c d c 
a chloritic slates ; b b quartz rock ; c c c white limestone ; d syenitic granite. 
A belt of syenitic granite is interposed between these limestones and another series of beds of 
limestone, alternating with quartz rock, coming to the surface near station 191. These are 
again succeeded by granite and hornblende slate of a compact texture, which, near one of the 
limestone beds, appears like a trap rock, breaking up into hard angular fragments, but still 
showing a distinct slaty structure. The section continues to present a succession of dark and 
light-colored syenites, passing into granite, in which the structural planes are developed in 
varying degrees to near station 206. At this point there is believed to be another outcrop of 
limestone ; one is recorded in section in the notes, but it is unaccompanied by any description 
except the mention of the presence of hornhlendic slates on each side. Whether this outcrop is 
at 206 or further east is uncertain. Its inclination, however, is towards the east. 
