Volume 2

Principles of geology : being an inquiry how far the former changes of the earth's surface are referable to causes now in operation. / By Charles Lyell ...

  • Charles Lyell
Date:
1834
Catalogue details

Licence: Public Domain Mark

Credit: Principles of geology : being an inquiry how far the former changes of the earth's surface are referable to causes now in operation. / By Charles Lyell ... Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

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    Ch. VII.] RELATIVE LEVEL OF DIFFERENT SEAS. I I the river first contracts itself, and is perceptible above Hoogly Town ; and so quick is its motion, that it hardly employs four hours in travelling from one to the other, though the distance is nearly seventy miles. At Calcutta it sometimes occasions an instantaneous rise of five feet; and both here, and in every other part of its track, the boats, on its approach, immediately quit the shore, and make for safety to the middle of the river. In the channels, between the islands in the mouth of the Megna, the height of the Bore is said to exceed twelve feet; and is so terrific in its appearance, and dangerous in its consequences, that no boat will venture to pass at spring tide.”* These waves may sometimes cause inundations, undermine cliffs, and still more frequently sweep away trees and land animals from low shores, whereby they may be carried down, and ultimately imbedded in fiuviatile or submarine deposits. Relative level of different seas.— There is another question, in regard to the effects of tides and currents, not yet fully determined — how far they may cause the mean level of the ocean to vary at particular parts of the coast. It has been supposed, that the waters of the Red Sea maintain a constant elevation of between four and five fathoms above the neighbouring waters of the Mediterranean, at all times of the tide; and that there is an equal, if not greater diversity, in the relative levels of the Atlantic and Pacific, on the opposite sides of the isthmus of Panama. But the levellings recently carried across that isthmus by Mr. Lloyd, to ascertain the relative height of the Pacific Ocean at Panama, and of the Atlantic at the mouth of the river Chagres, have shown, that the * Itennell, Phil. Trans. 1781.
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