chap. vin. Distribution of Gravel. 225 



Looking to the gravel on any one of the step-formed 

 plains, I cannot doubt, from the several reasons assigned 

 in this chapter, that it has been spread out and levelled 

 by the long-continued action of the sea, probably during 

 the slow rise of the land. The smooth and perfectly 

 rounded condition of the innumerable pebbles alone 

 would prove long-continued action. But how the whole 

 mass of shingle on the coast-plains has been transported 

 from the mountains of the interior, is another and more 

 difficult question. The following considerations, how- 

 ever, show that the sea by its ordinary action has con- 

 siderable power in distributing pebbles. A table has 

 already been given, showing how very uniformly and 

 gradually l the pebbles decrease in size with the gradu- 

 ally seaward increasing depth and distance. A series 

 of this kind irresistibly leads to the conclusion, that 

 the sea has the power of sifting and distributing the 

 loose matter on its bottom. According to Martin 

 White, 2 the bed of the British Channel is disturbed 

 during gales at depths of sixty-three and sixty-seven 

 fathoms, and at thirty fathoms, shingle and fragments 

 of shells are often deposited, afterwards to be carried 

 away again. Ground-swells, which are believed to be 



1 I may mention, that at the distance of 150 miles from the 

 Patagonian shore I carefully examined the minute-rounded particles 

 in the sand, and found them to be fusible like the porphyries of the 

 great shingle bed. I could even distinguish particles of the gall- 

 stone yellow porphyry. It was interesting to notice how gradually 

 the particles of white quartz increased, as we approached the Falk- 

 land Islands, which are thus constituted. In the whole line of 

 soundings between these islands and the coast of Patagonia dead or 

 living organic remains were most rare. On the relations between 

 the depth of water and the nature of the bottom, see Martin White 

 on ' Soundings in the Channel,' pp. 4, 6, 175 ; also Captain Beechey's 

 ' Voyage to the Pacific,' chap, xviii. 



2 'Soundings in the Channel,' pp. 4, 166. M. Siau states 

 (< Edin. New Phil. Jour.' vol. xxxi. p. 246), that he found the sedi- 

 ment, at a depth of 188 metres, arranged in ripples of different 

 degrees of fineness. There are some excellent discussions on this 

 and allied subjects in Sir H. De la Beche's ' Theoretical Researches.' 



