PORPHYRY. 
85 
the rock by waves, and also its interposition in the slate, makes it very clearly a rock which 
has been formed at a period subsequent to the consolidation of slate with which it is connected, 
and not by the successive depositions of particles from suspension in a watery medium. The 
apparent stratification is interesting in another point of view: it proves the liability of mis¬ 
taking this structure for a true stratification, in those cases where the means of detecting and 
correcting the error does not exist; as serpentine, basalt, greenstone, etc., all of which some¬ 
times exhibit divisional planes analogous to those exhibited by the porphyry at Cannon’s 
Point. 
The wood cut, (fig. 20,) represents the position of the porphyry at Cannon’s Point. The 
disturbed portion is seen on the left, and the regular columnar mass in the middle and upon the 
right. , What is particularly worthy of attention, is the slight alteration and disturbance which 
has followed from the injection of so large a mass of matter as appears in the slate at this 
place. 
In addition to what is seen of this rock along the shore of the lake, it appears in conside¬ 
rable force in the fields on the west side of the road, where it covers a. hundred acres or more, 
being apparently spread out over the slate and a portion of the Trenton limestone. It is quite 
broken and fragmentary in many places, presenting low cliffs, in the face of which there are 
a few rounded concretions. To the south about four miles, at a place known in the neighbor¬ 
hood as Rattlesnake's den, it appears in a bluff of from one hundred and fifty to two lumdred 
feet high. At this locality, it presents the same characters as at Cannon’s Point; and in 
consequence of its structure and its exposure, it has been broken into an immense quantity of 
pieces three or four inches in length and two in diameter, which have fallen down to the shore 
and formed a steep talus, over which it is extremely difficult to pass, in consequence of the 
loose state of the fragments which continually slide under the foot. 
Nature, Origin and Period of Formation of the Porphyry. 
If the porphyry appeared only at the last mentioned place, it would have been impossible 
to have spoken very definitely of the period when it was formed, as the rocks in which it is 
inclosed belong to the primary class ; but taken in connection with the slate of the Champlain 
