386 



NA TURE 



{March i8, 1875 



Origin of the Chesil Bank 



In your report (vol. xi. p. 299) of the paper on this subject by 

 Prof. Prestwich, read at the Institution of Civil Engineers, are 

 these words : — " The large dimensions of the bank he attributed 

 to the great accumulative and small lateral action of the waves." 

 Why, then, does' not so general a cause form hundreds of such 

 banks? Why is " the great accumulative action of the waves" 

 confine 1 solely to the Chesil Bank, and particularly to the Port- 

 land end of it ? Because the travelling of the pebbles is tinmrds 

 Portland, which checks the travelling, and so allows of "accu- 

 mulation " exactly as a gron does. This is the simple "open 

 sesame" of the secret ; and if we could build gioins as large as 

 Portland, every one of them would "accumulate" a I'ank of 

 precisely the same conditions as the Chesil Bank. If the peb- 

 bles travelled from Portland, as the professor thinks, that end of 

 the bank should be the lowest ; it would be perpetually robbed 

 by the w.ives. But it is the highest— lorty-three feet ; and the 

 Abbotsbury end, to which he supposes the pebbles to travel, 

 should be the highest, but it is the lowest— scarcely more than 

 half the height, twenty-three feet ; while at Eridport there 

 should be a still higher bank, fcr the professor makes the pebbles 

 travel from east to west there and meet the jiebbles which had 

 "travelled from the opposite direction, viz., from west to east." 

 But at Eridport there is not a single pebble, but only blown sand. 



That the largest pebbles accumulate at the leew.ard end of 

 beaches is not a matter of opinion, but a matter of fact, and the 

 fact may be iccn at every groin in the world. So that the large 

 pebbles at Portland, instead of testifying against the travelling 

 from west to east, Ie^tify conclusively for it. If there is anyone 

 who can suppose that the diminishing of the pebbles in size from 

 Portland to Abbotsbuiy results from the wearing in Iraveliing 

 that distance, there can be no one who could give this cause for 

 the same result between two groins. The cause which I have 

 assigned (chapter on " Travelling of Sea Beaches," Rain and 

 Rivers) for the lodgment of the largest pebbles at the Poitland 

 end, is that where motion is given to pebbles the largest will be 

 on the outside ; they are therefore most amenable to the upward 

 and onward stroke of the wave, and they travel fastest and 

 furthest down wind on these beaches. 



With regard to the modern beaches being recoinpositions of 

 ancient raised beaches, besides the travelling, their pebbles are 

 perpetually pounded by the waves till they are ground into sand. 

 The professor dates the Portland raised beach to the Glacial 

 Pericd. We have ample time, then, for its pebbles to be ground 

 into sand and replaced by new comers. And the new recruits 

 would not come, as the professor thinks, solely from " the cliffs," 

 but chiefly from the mouths of the rivers which bring pebbles 

 from all the various strata of the interior of the land without the 

 aid of ice ; for atmospheric disintegration and the erosion of 

 rain denude the entire surface of the earth, and let down to the 

 rivers not only soft soil but hard gravels and stones from every 

 the most remote hill-top. But this huge traffic is brought to the 

 rivers by rain. Rivers are simply the roads which it travels to 

 the sei. What is held in suspension goes out to deep water, but 

 the gravels, stones, and boulders are pounded arid ground into 

 the sands of the sea-shore. George Greenwood 



Alresfqrd, March 2. 



Natural Phenomena in South America 



In Mr. J. IWunro's very interesting notes made during a cable- 

 laying expedition from Para to Cayenne, which were published 

 in Nature, vol. xi. p. 329, the following passage occurs upon 

 which comment may be useful. After describing a beautifully 

 coloured Crustacean, and an animal which he speaks of as a crab 

 or water-beetle, Mr. Munro goes on to say : "Another creature 

 (Fig. 3) of quite a different description was also picked up. It 

 was more like a water-spider than anything else. Its transparent 

 hair-like limbs were dappled with dull green, and it seemed a 

 mere skeleton framework made to carry a small white sac con- 

 taining entrails, which was slung underneath." From the figure 

 it is tolerably evident that this creature is one of the Pycnogonldre, 

 whose place in a classification of the animal kingdom is scarcely 

 yet definitely settled, but which are ranged by Prof Milne- 

 Edwards among Crustaceans. It seems highly probable, then, 

 that "the small white sac containing entrails" should rather 

 have been described as a pair of very slender legs carrying egg- 

 bags. This at least would be in accordance with what is known 

 of other species of Pyciiogons, none of which carry their entrails 

 in sacs slung underneath. 



The delicate spider-crab (Fig. l), which charmed Mr. Munro 

 with its hyaline limbs and varied colouring, seems from the figure 

 to be nearly allied to the genus Stenorhynchus. 



The affinities of Fig. 2 cannot be guessed at without additional 

 details. 



It is likely enough that all the creatures mentioned may be 

 specifically new. Thomas R. R. Stebbing 



Torquay, March 10 



Volcanic Action in the Sandwich Islands 

 In your notice of my book, "The Hawaiian Archipelago," 

 (vol. xi.p. 322), you a'ludeto the statement that volcanic action on 

 the Sandwich Islands " has died out from west to east." It has 

 also died out in a soutlicrly direcdon, through nearly four degrees 

 of latitude. In the pit of Hale-mau-mau within the crater of 

 Kilauea, nn January 30, 1873, the violently agitated mass of 

 lava continually took a southward direction, and broke in very 

 elevated surges upon the cliffs on the south side of the lake. 

 On June 4, 1S73, when ihe aspect of the pit had undergone a 

 very great change, there was a violent centripetal action, but the 

 sort of rotating whirlpool continually formed, invariably rotated 

 in a souihaiy direction. Some years ago, during a terrible erup- 

 tion of Kilauea, when a river of lava from 200 to Soo feet wide, 

 and an estimated depth of twenty feet, was running towards the 

 sea with an estimated velocity of twenty-five miles an hour, four 

 large " fire-fountains" boiled up when the stream issued from 

 the earth. An intelligent observer, Mr. Whitney, noticed that 

 the lava was ejected with a rotary motion, and that both the lava 

 and stones thrown up rotated towa>-ds the south. I should be 

 very glad to know any probable explanation of these phenomena, 

 and if this apparently persistent southerly extinction and motion 

 have any and what value as scientific facts ? 



Mr. Munro (vol. xi. p. 329) describes the locking together of 

 trees of different species in the neighbourhood of Para. The 

 instances of this in the Hamakua forest on Hawaii are very 

 numerous and striking. The Ohia [Mcli-osiJeros polyinorpha ?) 

 is seen in the closest conjunction with the large tree-fern of the 

 district, with a universality which leads some people of more 

 than average intelligence to assert dogmatically that the fern is 

 the invariable parent of the Ohia ! The junction is so intimate 

 as to be apparent interpenetration. The greatest height of any 

 tree-fern that I have measured is eighteen feet of caudex; but I 

 have seen Ohias with an estimated height of eighty or ninety feet 

 carry the tree-fern with them to a height of fully thirty feet, the 

 fresh pea-green fronds branching out from among the dark leaves 

 and deep red blossoms of this very handsome evergreen. 

 6, Alva Street, Edinburgh, March 3 Isabella L. Bird 



The Height of Waves 



The height of waves has long been a vexed question amongst 

 all classes of theoretical and practical observers. The late 

 Admiral Fitzroy has left on record that on one occasion the 

 measurement from crest to hollow was seventy feet. The figure 

 seems high, but close and varied observations made during a 

 storm on the passage from Liverpool to New York, in January, 

 convinces me of the correctness of the Admiral's statement. In 

 this storm, for the first time on record, large ocean steamers 

 were rounded to with a fair wind, the universal opinion being 

 that it was too dangerous to run with the sea far on the quarter. 

 The captain of a German steamer, on arriving at New York, 

 spoke in enthusiastic terms of the grand spectacle a White Star 

 steamship presented as she "leaped from wave to w.ave like 3 

 gigantic fish," adding : " I am sure she must have hove to in the 

 end." 



This remarkable gale swept over a portion of the Atlantic 

 which the French call " Le irou de diable," and it well merits 

 the designation. Roughly, its focus may be considered to be in 

 45° N. and 40° W. When the wind sets in strongly from the 

 north-west, the sea rises in an incredibly short space of time; 

 and at the close of a long winter gale it is a grand sight to watch 

 the great waves as they roll up astern at the rate of twenty-five 

 miles per hour, sweep by the ship, and break far ahead. There 

 is a feature in connection with the wave> of the Atlantic which is 

 worthy of notice, viz., with a south-west or southerly gale their 

 height is insignificant. A practical proof of this is that large 

 steamers run in the trough of the sea without inconvenience ; but 

 with less wind from the north-west they have occasionally to be 

 kept off their course to avoid damage to boats. What occasions 

 this remarkable phenomenon? It cannot be the "fetch," as seamen 



