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II.—Observations on the Rounding of Pebbles by Alpine Rivers, with a Note on their Bearing upon the Origin of the Bunter Conglomerate1
Published online by Cambridge University Press: 01 May 2009
Extract
When preparing my address to Section C in 1886, I had much need of information as to the amount of rounding which takes place in rock fragments when transported by rapid streams. Useful information and references are given in Dr. A. Geikie's Text Book and in De Lapparent's “Traité de Géologie,” and there are the experimental researches of Daubrée in his “Géologie Experimental”; but from neither these nor other sources (so far as known to me) could I obtain what I wanted. I must, however, admit that I am less familiar with the talus heap of geological literature than I should be, and prefer making observations in the open air, to hunting for records of them in a library. So, as I had some opportunities of doing the former during my journey last summer, I record the results in the hope that they may be useful to others; first heartily thanking my companion, the Rev. E. Hill, for constant co-operation and assistance.
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References
page 54 note 2 Book iii. pt. ii. sec. ii.
page 54 note 3 Book ii. sec. i. ch. iii.
page 55 note 1 Vol. i. sec. ii. ch.
page 56 note 1 Distances in this paper, unless otherwise stated, are measured on a map, and so are obviously less than the actual course of the stream.
page 57 note 1 It must be remembered that when a torrent descends precipitously over a bed of rock, not a few stones may receive an exceptional amount of rounding by being whirled about in ‘potholes.’
page 58 note 1 Our estimates of the rates of flow varied from about three to four and three quarter miles an hour. I expect these great mountain rivers run at an average pace of nearly four miles an hour, and at certain seasons considerably exceed this.
page 58 note 2 I mean as fairly strong streams; in some cases brooklets would be higher, and of course the snow-beds about the sources of the Po rise up in places to quite 9000 feet.
page 60 note 1 ProfDaubrée, (Géol. Experim. vol. i. sec. ii. ch. v.)Google Scholar obtained experimentally a distance of a little less than 16 miles for the manufacture of a rounded pebble of granite, but this must be regarded as the least possible distance, for in his experiments the fragments would be knocked one against another much more than in transport by a stream, except perhaps in a “pothole.”
page 61 note 1 Geol. Mag. Dec. II. Vol. X. p. 285.Google Scholar
page 61 note 2 Proc. Phil. Soc. Birmingham, vol. iii. p. 157Google Scholar; Geol. Mag. Dec. II. Vol. X, p. 199.Google Scholar This locality is practically included in the other.