2i6 THE SEA FLOOR 



Minerals (i-oo per cent.). — Mean diameter o- 06 mm., 

 angular ; felspar, hornblende, magnetite, magnetic 

 spherules, pumice, a few manganese grains, bronzite 

 spherules. 



Fine Washings (5-46 per cent.). — Amorphous matter, 

 with small mineral particles, and fragments of scoriae 

 and siliceous organisms. 



Remarks. — This is one of the purest Globigerina 

 oozes obtained by the " Challenger," and is almost 

 wholly composed of the dead shells of surface organisms. 

 A few pumice fragments were found in the washings of 

 a large quantity of deposit. 



When carbonate of lime is present, the shells and 

 other calcareous organic fragments are determined by 

 microscopic examination. The lime is then removed 

 from the sample by weak hydrochloric acid, and the 

 relative percentages of lime and residue can be approxi- 

 mately estimated by inspection, or determined by a 

 simple analysis. The nature and relative abundance 

 of the clayey matter, mineral particles, and remains 

 of siliceous organisms in the residue can be estimated 

 by microscopic examination. A description of this 

 kind can quite easily be carried out on board ship. 



The following is a short description of the principal 

 types of deep-sea deposits : 



A. — Pelagic Deposits. 



1. Red Clay. — This deposit is the most characteristic, 

 and probably the most widely distributed, of all deep- 

 sea deposits over the ocean's floor, covering a very large 

 portion of the deeper parts of the Pacific. The name is 

 sufficiently expressive of the nature and appearance of 

 this type of deposit, there being always a considerable 



