Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/82

 Mr. Mallet had remarked that nearly all river-courses are in longitudinal section hollow curves which do, in their upper reaches at least, appear to present more or less of the character of parabolas. But although the well-known formula which expresses the discharge at each point, and in fact the regimen of the stream, might seem a priori to countenance the idea that these curves are parabolic, he is much disposed to think that the form of water- channel does not depend upon any hydrodynamic law, but simply upon the natural contour of the longitudinal sections of the river- courses, which run almost always on the bare rocky skeleton of the earth, and follow the forms, viewed on a broad scale, of all rocky anticlinals, whose slopes are always more or less hollow curves. As regards the long gently sloped lower reaches of all rivers, and more particularly of great rivers, such as those appealed to by the author, Mr. Mallet believed that it would be perfectly impossible to affirm that their longitudinal sections conformed to any particular curve. When plotted, such sections will be found to fit equally well to right lines, or, if curved, to parabolas, ellipses, arcs of circles, or what we please.

Mr. Tylor replied that he had not found definite evidence as to the extension of corals downwards to such a depth as that mentioned by the President. With regard to oscillation, he had merely treated of the southern part of England. The opening of the Straits of Dover would account for the existence of beaches above the present level, as the tides would have previously risen higher. The parabolic curve was that which, by actual comparison, coincided most closely with the longitudinal section of the banks of the rivers Po, Mississippi, and Ganges.

November 25th, 1868.

The following communications were read : —

1. On Floods in the Island of Bequia. By G. M. Browne, Esq. (Communicated by the Secretary of State for Foreign Affairs.)

[Abstract.]

On the 17th of March, at 8 o'clock p.m., a steady strong wave was seen bearing down upon Admiralty Bay ; it had no perceptible crest, and was 3 feet in height ; it encroached upon the land to distances varying from 70 to 350 feet. A second, smaller wave followed. No shock of an earthquake was felt.

Discussion.

Dr. Duncan wished for some explanation of these earthquake - waves, more especially with regard to the effects of supposed cataclysmic waves. He considered that they arose from sudden changes in the level of shoals or littoral tracts, and not from deep-sea disturbances.