1882.] 



On the Formation of Iilpplemarh. 



9 



out from under the old, owing to the edges having been too much 

 damaged to admit of continuous shell formation, it may be contended 

 that the individual mollusc had met with some special accident, but 

 when hundreds of cockles are dredged together, showing the same 

 marks of damage, repair, and subsequent growth, it is impossible to 

 escape from the conclusion that they were all subjected together to 

 some serious disturbance of their beds. 



In a paper read to the Devonshire Association, in 1878,* I showed, 

 from the data furnished me by Lord Rayleigh, that on the 6-fathom 

 area in Torbay a wave 300 feet long and three feet above mean level, 

 if such ever occurred, would cause an alternating current at the bottom 

 with a maximum speed of 3 feet per second. On two occasions 

 (22nd October, 1880. and 4th April, 1881), since then, during easterly 

 gales, I have observed waves with a period of 8f seconds, and on one 

 occasion, viz., on the 19th October, 1881, waves with a period of 

 8 seconds. On the last occasion, as has been already stated, I was 

 able, by means of known marks to measure both the wave-length and 

 speed. The length where measured proved to be 275 feet and the 

 speed 660 yards per minute, but as the w T aves, before reaching the 

 shore had to traverse about 1,000 yards of water less than 6 fathoms 

 in depth, their length in midbay probably did not fall short of 

 300 feet. Their height I had no means of measuring, but at the low 

 computation of one-thirtieth the wave-length, it would be 10, feet, or 

 5 feet above mean level. f 



Leaving Torbay, with its comparatively shallow water, I will 

 proceed to examine the evidence of disturbance at the bottom, in the 

 deeper waters of the English Channel. The evidence at hand is of a 

 varied nature, and includes the testimony borne by the character of 

 the bottom itself, by valves of shells and other inanimate objects 

 dredged up, by the character of the fauna, and by experienced fisher- 

 men. 



In April, 1880, a large earthenware jar was brought up in the 

 trawl of the Brixham smack " Pelican " about 20 miles south-east of 

 the Start point, where the depth, according to the chart, is about 36 or 

 37 fathoms. 



Mr. Pengelly, F.R.S., has described this jar with its contents (as 

 received at Torquay) of half-a-pint of sand and gravel, and from the 

 fact that " the whole surface of the bottom, as well as about fully one- 

 half of the entire lateral surface " was covered with marine organisms 

 and that the jar was not abraded, arrived at the conclusion " that the 



* " Trans. Dev. Assoc.," vol. x, p. 192. 



f On the 25th October, -when the weather had moderated, H.M.S. " Inflexible " 

 left Plymouth for Gibraltar. On her arrival there, Captain Fisher reported having 

 encountered waves 300 feet in length and 24 feet in height. — (" Western Morning 

 News.") 



