256 On the Geography and Geology 



gular fact is the intersection of this point, three or four yards from 

 the scarp above noticed, by a trap vein, or dyke, about a foot 

 thick. It mounts the rocky point from the lake, like a flight of 

 steps, and is lost in the shrubbery contiguous. It is represented 

 in the annexed sketch by a zigzag line; — not quite in place. 



Close on the S.W, of this point (on the way to Fort Wil- 

 liam) are other small layers of this limestone, horizontal, and in- 

 terleaved with a seam or two of the red shale of the scarp ; and 

 in a cove three- fourths of a mile further S.W., this red sandstone 

 overlies the grey limestone; for such I suppose this last stratum, 

 although I have not had an opportunity of testing it by acids. It 

 is frequently seen both under and over the red sandstone, and by 

 itself, in the rocky ledges emerging from under the small beaches 

 of this coast. About mid-way between the first-mentioned point 

 and Thunder Point, a broken ridge of greenstone trap cuts through 

 these horizontal rocks ; which, however, soon recur westwards for 

 500 yards, and are then replaced by the trap nearly to Thunder 

 Point in the form of a wall of moderate and varying elevation, 

 washed by the waves, and supporting the ascent of broken terraces 

 at the foot of the mountain. This trap contains several patches 

 of conglomerate, whose large black nodules are imbedded in a dark 

 and, probably, trappose cement. The exact nature of this conglo- 

 merate and its relation to its enclosing rock I am ignorant of. 

 Three quarters of a mile from Thunder Point, ragged angular 

 masses of slaty rocks (almost certainly sandstone), ten, twenty, 

 and thirty feet in diameter are completely enveloped in the trap ; in 

 accidental positions, as indicated by the direction of their layers. 

 The above distances are conjectural ; but the appearances just men- 

 tioned, are so striking, that they cannot well pass unnoticed. 

 Near Thunder Point there are reefs, (besides others on this side of 

 the mountain) rising out of the lake in fixed blocks of dark gray 

 sienite, or rather of greenstone trap, whose feldspar is in visible 

 white grains. It lines the adjacent point in large quantities of 

 angular debris mingled with the common form of the latter rock, 

 and sandstone, amygdaloid, limestone, ^-c. Hare Island in Thunder 

 Bay, consists of this sienite, but the feldspar is neither so distinct 



