EASTERN PACIFIC EXPEDITION 427 



volcanic rocks and minerals, principally pumice, the pro- 

 ducts of both aerial and submarine eruptions. In desert 

 regions, where little else accumulates on the bottom, 

 these volcanic products are exposed for a long time to 

 the action of sea- water and thus undergo alteration. The 

 manganese contained in them is converted into bicar- 

 bonate of manganese, which is deposited as manganese 

 dioxide upon coming into contact with the overlying 

 water. The deposition usually takes place around a 

 nucleus, which may be a shark's tooth, an ear-bone of a 

 whale, or a decomposing fragment of volcanic glass, 

 though in some cases no nucleus can be detected. 



As the Albatross neared Easter Island, Agassiz be- 

 came very anxious about meeting his collier, supposed 

 to be approaching this isolated spot from the other end 

 of the world. Any failure on her part would, indeed, 

 have proved a very serious matter, for there is no com- 

 munication with the island except about once a year, 

 when a Chilian man-of-war calls there. As the ship 

 approached Cook Bay, every one was eagerly looking 

 ahead. On rounding the promontory, not only did the 

 collier come into view, but to their intense surprise a 

 Chilian man-of-war, whose captain Agassiz suspected 

 had somehow got wind of the expedition and turned up 

 there to see what was going on. 



TO MRS. G. R. AGASSIZ 



On Board the Albatross, 



Easter Island, Dec. 17, 1904. 



Little did I think that on my 69th birthday I should 

 be writing you from such an out-of-the-way place ! We 

 arrived here the 15th after an excellent trip from Callao ; 

 the Captain of the collier was on board almost before 



