on board H.M.S. e Challenger, 3 ' 521 







Green Muds. 







fms. 



fms. 



fms. 



fms. 



fms. 



470 



2200 



400 



129 



37 



560 



290 



10 



255 



152 



80 



120 



70 



100 



245 



75 



650 



800 



705 



565 



100 



950 



580 



185 



775 



150 



1200 









(b) Grey Muds and Sands. — -Near volcanic islands we have found that 

 the deposits have a distinctive character, from the presence o£ the debris 

 of volcanic rocks. The presence of pieces of pumice, scoria, &c. prevents 

 this deposit having that clayey character so characteristic of the blue 

 mud. The colour is generally grey, but occasionally is a black sand or 

 a more or less slate-coloured mud. In some places the shells of oceanic 

 organisms make up a large part of these muds. 



Down to about 1500 fathoms we have Pteropod, Heteropod, and sur- 

 face G-asteropod shells, and the shore forms of Foraminifera are common. 

 Deeper than 1500 fathoms, Pteropod shells are rare or entirely removed. 

 Pelagic Foraruinifera are found at all depths ; but occasionally they and 

 the siliceous organisms are quite absent at a depth of little over 2000 

 fathoms, and then we have a clay or mud with many small particles of 

 pumice, scoria, &c. Manganese appears to be intimately associated with 

 some of these bottoms, especially where the debris of augitic lavas are 

 present, as at Sandwich Islands, Canaries, and elsewhere. Off: the 

 Desertas, in 670 fathoms, all the dead shells, pieces of Polyzoa, &c. had 

 a slight coating of this substance, and we have had indications of the 

 same thing in even less depths. In 1100 fathoms off the Canaries some 

 pieces of shell had rather a thick coating ; and in 1575 fathoms, not far 

 from this place, the dredge brought up a great quantity of a Gorgonoid 

 axis deeply imbedded in or coated with this black oxide of manganese. 



In some localities this deposit extends to a great distance from the 

 islands, as at Hawaii, 200 miles or more. 



The following are the depths of the soundings which we have classed as 







Grey Mud. 







fms. 



fms. 



fms. 



fms. 



fms. 



670 



1750 



1675 (?) 



20 to 100 



500 



1150 



620 



465 



75 



2050 



930 



1890 



675 



520 



2875 



1500 



1525 



260 



630 



2650 



278 



450 



360 



600 



1525 



630 



1000 



1100 



1200 



420 



560 



1125 



50 



2150 



590 



7 



1070 



150 



2600 



620 



640 



1000 



600 



1050 



680 



Occasionally a few casts of the Foraminifera have been observed of a 



