278 
GEOLOGY OF THE SECOND DISTRICT. 
From the preceding remarks, it will be understood that this rock has less thickness in this 
county than usual, but still it is to be regarded as a mass very well characterized. In pur¬ 
suing the geology, however, of this valley, this rock is an important member in this series, 
and it is sufficiently well brought out to preserve the order and relations of the masses in this 
particular field. 
Utica Slate. 
This rock being only partially exposed, and occupying only some of the most depressed 
portions of the county, cannot be so fully described as some of the lower rocks of the Cham¬ 
plain group. It appears first near Split-rock, occupying the southern side of Whallon’s bay. 
At this place it lies against or upon the primary, in consequence of its extension in a particu¬ 
lar direction; or it appears here, as along some other extended lines, to overlap the rocks 
beneath, and to rest visibly upon the primary; that portion only which extends beyond the 
masses beneath it, being in contact with the oldest or Primary system. 
This mass at Split-rock is worthy of examination, in consequence of the curvatures in the 
strata at the line of junction; from which it appears, that since the consolidation of the slate, 
this portion of the Primary system has been elevated at least in part. 
Proceeding along the shore, we find the remains of a porphyry dyke in imperfect columns 
in the slate. No change in the texture or structure of the slate appears. The Triarthus, 
and numerous specimens of Graptolites which arc found within one or two inches of the 
porphyry, appear as in the same mass when remote from a plutonic rock. Neither are the 
layers disturbed or contorted, in the vicinity of this injected rock. 
We may trace the utica slate on the shore as far as the uplift of the chazy limestone, a 
distance of a mile. After leaving this mass, which contains the porphyry, we soon find it 
disturbed. It now dips on this shore in all directions, and its layers are more or less bent. 
When it comes in contact with the chazy limestone, as has been described, it is injected with 
numerous trap dykes, and traversed by veins of calcareous spar. 
After this interruption by the disturbances at this place, the utica slate does not appear until 
about half a mile north of Essex. It there occupies the whole shore as far as Peru bay. It 
forms only low banks, and here is barely exposed, so that we see merely the upper surface. 
Two miles north, it is more exposed near the road than along the shore, by a small stream 
which has cut a channel through it for seventy or eighty rods. At this place, it is again tra¬ 
versed by several dykes, one of which is a porphyry resembling that near Split-rock, and at 
Canon’s point. 
After searching a long time for fossils in this mass, I was unable to find any; though from 
its being disturbed, the unsuccessful search does not prove their absence. 
This rock is the highest in the scries in this county, and it is confined to Essex and the 
lake shore for a few miles north. In it we find no important mineral substances, and inas¬ 
much as it is brittle and subject to decomposition, it is never suitable for roofing. After 
drying, and then being moistened, it is liable to crack and fall to pieces; and by a want of 
cohesion, it is generally channelled out by small streams which flow over it. 
