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V.—On the Pitch Lake of Trinidad

Published online by Cambridge University Press:  01 May 2009

S. F. Peckham
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Extract

Near the crest of the ascent to the lake the road divides: one branch passing to the left and south ascends over the rim of the basin of the lake, and skirting the lake for about a quarter of its circumference passes over the hill to the south-west, as described by Mr. Manross. The right-hand branch follows the flow of the pitch and enters upon the lake simply by a change of grade from a sharp ascent to a very slight inclination upwards towards the centre of the lake. I was particularly impressed with this fact, and took pains to verify my first impression upon a second visit, as it proved conclusively that, notwithstanding the vast quantities of pitch that had been removed from the lake, there is still a movement out of the lake, glacier-like, down the slope to the sea.

Type
Original Articles
Information
Geological Magazine , Volume 2 , Issue 10 , October 1895 , pp. 452 - 458
Copyright
Copyright © Cambridge University Press 1895

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References

page 452 note 1 Dated 25th July, 1895.

page 452 note 2 On the Jurassic table-land of the Cotteswolds we find round quartzite pebbles, washed out of the New Red Conglomerate of the Midlands, scattered over the surface up to a level of about 600 feet—a real “Northern drift.”

page 454 note 1 Guppy says (Quart. Journ. Geol. Soc., xlviii, 527, note): “When a piece of the foraminiferal rock is placed in water, it absorbs it rapidly and falls asunder, and the water which enters into union with it is given up only to evaporation…. From these properties it follows that the natural soil roads passing over these rocks become in the wet season the worst quagmires it is possible to imagine.” Of another bed, “In the presence of water this rock is the most incoherent of any I have ever met with… It falls into powder at the mere contact of water.”

page 456 note 1 Proc. Amer. Philos. Soc., vol.x, p. 445Google Scholar. Bischoff, Chem. and Phys. Geol. (Cav. Soc. Ed.), ii, p. 28; ibid., vol. i, pp. 15, 340. T. S. Hunt, Chem. and Geol. Essays, pp. 23, 87, 99, 111.

page 456 note 2 Mr. Richardson asserts that 90 per cent. of the 80 per cent. of insoluble mineral matter in the pitch is silica. As a possible explanation of the presence of so much silica, I would suggest that the hot water that distilled the bitumen might have held silica in solution, which has been precipitated within the pitch as it has cooled. The fact, if it be a fact, that so much silica exists in the pitch as hydrate, may account for the large amount of water held in the pitch.