226 Distribution of Gravel. paet n. 



caused by distant gales, seem especially to affect the 

 bottom : at such times, according to Sir K. Schom- 

 burgk, 1 the sea to a great distance round the West 

 Indian Islands, at depths from five to fifteen fathoms, 

 becomes discoloured, and even the anchors of vessels 

 have been moved. There are, however, some difficulties 

 in understanding how the sea can transport pebbles 

 lying at the bottom, for, from experiments instituted 

 on the power of running water, it would appear that 

 the currents of the sea have not sufficient velocity to 

 move stones of even moderate size : moreover, I have 

 repeatedly found in the most exposed situations that 

 the pebbles which lie at the bottom are encrusted with 

 full-grown living corallines, furnished with the most 

 delicate, yet unbroken spines : for instance, in ten 

 fathoms water off the mouth of the Santa Cruz, many 

 pebbles, under half an inch in diameter, were thus 

 coated with Flustracean zoophytes. 2 Hence we must 

 conclude that these pebbles are not often violently dis- 

 turbed : it should, however, be borne in mind that the 

 growth of corallines is rapid. The view, propounded 

 by Prof. Playfair, will, I believe, explain this apparent 

 difficulty, — namely, that from the undulations of the 

 sea tending to lift up and down pebbles or other loose 

 bodies at the bottom, such are liable, when thus quite 

 or partially raised, to be moved even by a very small 



1 'Journal of Eoj^al Geograph. Soc.'vol. v. p. 25. It appears from 

 Mr. Scott Kussell's investigations (see Mr. Murchison's ' Anniver. 

 Address Geolog. Soc' 1813, p. 40), that in waves of translation the 

 motion of the particles of water is nearly as great at the bottom as 

 at the top. 



' A pebble, one and a half inch square and half an inch thick, was 

 given me, dredged up from twenty-seven fathoms depth off the west- 

 ern end of the Falkland Islands, where the sea is remarkably stormy, 

 and subject to "violent tides. This pebble was encrusted on all sides 

 by a delicate living coralline. I have seen many pebbles from depths 

 between forty and seventy fathoms thus encrusted ; one from the 

 latter depth off Cape Horn. 



