230 
[Assembly 
It is unnecessary to comment on phenomena of this character in this 
place, only so far as to say, that it is evident that the dykes of Juniper 
Island are more recent than those at the point and at Whaling's Bay, 
inasmuch as the vertical one produced an upard movement of the slate 
and the horizontal or distinct lateral movement, while those at the two 
last mentioned places have not disturbed the slate at all. 
Sandstone of Essex, 
This I consider the same formation I have described under the name 
of the " Potsdam Sandstone." 
Its position is evidently beneath the transition limestone and calcife- 
rous sand rock. It is very deficient in organic relics, though not en- 
tirely destitute of them. It is unnecessary to repeat what has already 
been said of this rock; it is purely quartzose or siliceous in its compo- 
sition, and finely stratified. It dips to the northeast at Port Kent, at 
an angle varying fr^m 5 to 10°. The places where it occurs along 
Lake Champlain are indicated on the map of a part of this county, to 
which I refer the reader. This rock at Keeseville has been rent in the 
most remarkable manner; several fissures, the principal one of which 
extends nearly a mile, and through which the Ausable flows, have been 
opened by some convulsion in nature to the depth, in some places, of 
a hundred feet, and from five to twenty wide. Near the bottom of the 
fissure at the High Bridge, as it is called, I discovered numerous speci- 
mens of a small bivalve molusca, a lingula. I found also, on exami- 
nation, that the same fossil occurred through an extent of seventy feet 
at least, and so far as I could discover, it was the only fossil enclosed in 
the rock. It is extremely thin and delicate, yet the shell is perfectly 
preserved, and is probably one of the oldest inhabitants of the globe, 
as the rock in which they occur is the oldest of the transition series. 
Another phenomenon of some interest, which may be seen at the 
depth of 70 or 80 feet in this sandstone, are ripple marks. This fact 
does not appear quite consistent with the received opinion that ripple 
marks are made only in very shallow seas, for it appears more consis- 
tent with reason to suppose that this vast stratum of sandstone must 
have been deposited in a sea of great depth. It is a question, however, 
diflScult to solve. 
As a natural curiosity, the High Bridge of Keeseville is worth a visit 
from the traveller; it is truly one of the wonders of the northern dis- 
trict. Besides presenting a grand view of strata superimposed one up- 
on another, it opens an interesting field for reflection on the nature of 
