CHAP, v.] GENERAL CONCLUSIONS. 255 



was a very lieavy fall of rain, such as had not been experienced 

 by the inhabitants for many years. For several days after, 

 many pieces of scoria?, cinders, and the like were noticed float- 

 ing about on the surface of the sea near the island. Such frag- 

 ments may be transported to great distances by currents. 



On the shores of Bermudas, where the rock is composed of 

 blown calcareous sand, we picked up fragments of traveled vol- 

 canic rocks. The same observation was made by General Nel- 

 son at the Bahamas. Mr. Darwin observed pieces of pumice on 

 the shore of Patagonia, and Professor L. Agassiz and his com- 

 ]>anions noticed them on the reefs of Brazil. During a recent 

 eruption in Iceland, the ferry of a river is said to have been 

 blocked for several days by the large quantity of pumice float- 

 ing down the river and out to sea. 



Near volcanic centres, and sometimes at great distances from 

 land, we find much volcanic matter in a very fine state of di- 

 vision at the bottom of the sea. This consists mainly of mi- 

 nute particles of feldspar, hornblende, augite, olivine, magnet- 

 ite, and other volcanic minerals. These particles may probably 

 have been in many cases carried to the areas where they are 

 found by winds in the form known as volcanic dust or ashes. 

 Mr. Murray examined a packet, sent to me by Sir Rawson Raw- 

 son, of volcanic ashes which fell at Barbadoes in 1812, after 

 an eruption on the Island of St. Yincent, a hundred and sixty 

 miles distant ; and he found them to be made up of particles 

 similar to those to which I have referred. 



The clay which covers, broadly speaking, the bottom of the 

 sea at depths greater than 2000 fathoms, Mr. Murray considers 

 to be produced, as we know most other clays to be, by the de- 

 composition of feldspathic minerals ; and I now believe that 

 he is in the main right. I can not, however, doubt that were 

 pumice and other volcanic products entirely absent, there would 

 still be an impalpable rain over the ocean-floor of the mineral 

 matter which we know must be set free, and must enter into 



