on board H.M.S.' Challenger.' 519 



sea-deposits and at all depths in more or less abundance. However, for 

 the present, it has been considered best to treat of its occurrence sepa- 

 rately, at the some time pointing out those regions where we have found 

 it in greatest abundance. 



A few remarks may now be made upon each of the kinds of deposits 

 indicated. 



1. Shore-deposits. — It has been found that the deposits taking place 

 near continents and islands have received their chief characteristic from 

 the presence of the debris of adjacent lands. In some cases these depo- 

 sits extend to a distance of over 150 miles from the coast. Several 

 varieties can be recognized amongst these shore-deposits. 



(a) Blue and Green Muds. — In the great majority of cases the deposits 

 near continents and large islands, containing the older and crystalline 

 rocks, have been of a blue or green colour ; the only exception appears 

 to be the east coast of South America, where we have a red mud, to be 

 presently referred to. 



In from 100 to 700 fathoms these deposits are often of a green colour, 

 due to the presence of green amorphous clayey matter, and dark and pale 

 green glauconite particles. 



Beyond 700 fathoms they are usually of a blue or dark slate-colour, 

 having a thin upper layer of a red or brown. This red layer is a soft 

 ooze, whilst the blue mud or clay beneath is very compact and tenacious. 



Much amorphous clayey matter and fine particles of mica, quartz, and 

 other minerals are found in all these deposits, the mineral particles in- 

 creasing in size as we approach the land. 



Down to 1500 fathoms, we have generally found that Pteropod, larval 

 Gasteropod, and Lamellibranch shells were tolerably abundant, and that 

 there were many of the shore forms of Foraminifera, as Textularias, Bo- 

 tularias, Nodosarias, Uvigerinas, Lagenas, &c. Pelagic Foraminifera occur 

 throughout the deposit, but not in such abandance as in a true ocean- 

 deposit. The frustules of Diatoms and their broken parts are numerous. 

 Manganese grains are found in many of the bottoms, usually in the 

 deeper soundings. "We have also found imbedded in these muds pieces 

 of wood, fruits, portions of fruits, and leaves of trees. Large pieces of 

 rock, as pumice and granite, and rounded pebbles also occur. Our sound- 

 ings near the southern ice-barrier were muds of a blue colour, containing 

 many granitic and other pebbles and blocks, mostly rounded, and many 

 Diatoms, and resembled in most respects the deposits we found off the 

 east coast of North America, Halifax to New York. 



Beyond 1500 or 1700 fathoms, Pteropod and Heteropod shells are 

 usually not found, and in 3000 fathoms hardly a Poraminiferous or other 

 carbonate-of-lime organism remains. 



Siliceous organisms occur at all depths, but at times their remains 

 would seem to be completely removed. 



These green and blue muds have been found to prevail in all the en- 



