THE DEPTH AND MARINE DEPOSITS OE THE PACIFIC OCEAN. 21 



so finely comminuted as to appear quite amorphous under the microscope. 

 Phillipsite in minute crystals is also present, and this is not the least inter- 

 esting point in the deposit. As regards the origin of this mud there is no 

 evidence at hand to show exactly what it is, but according to the prelimi- 

 nary report the sounding comes after a series of soundings which had revealed 

 the presence of Coral Sand, in the vicinity of Manga Reva, in depths ranging 

 from 225 to 1394 fathoms; this mud may thus possibly represent a very 

 finely comminuted Coral Mud, the finer parts of which have been carried to 

 the place where they were deposited, in a depth of 2225 fathoms. Refer- 

 ence to the description will show that the calcareous constituents of this 

 deposit are so minute that there is no mechanical objection to the supposition 

 that they may have been held in suspension in the water and carried away a 

 certain distance from their point of origin. It must be observed, however, 

 that there is no known coral reef within 150 miles of this position. 



Volcanic Sand. A typical sample of this deposit was brought up from 

 1552 fathoms, off Easter Island. 



The Mineral Constituents Observed in the Different Deposits. 



The mineral constituents in the Globigerina Oozes found by the " Alba- 

 tross " are, as a rule, very small.^ When estimating the percentage of 

 minerals, the plan adopted by the authors of the Challenger Report on 

 Deep-Sea Deposits was adhered to ; that is to say, particles that are not 

 washed away together with the fine clay are put down as " minerals." 

 These were weighed, and the percentage estimated after deducting the 

 amount of siliceous organisms as indicated later. In two cases no mineral 

 particles were observed ; in twenty-two cases the minerals were estimated 

 as traces; in six cases the percentage is estimated at less than 1, and in the 

 remaining six the percentage varies from 1 to 5. This fact is easily ac- 

 counted for, as the ooze extends in a broad tract far from land, where the 

 greater part of the mineral particles have a volcanic origin, continental 

 debris being only accidentally met with. 



Augite, plagioclase, volcanic glass, and magnetite are the minerals that usu- 

 ally accompany Globigerina Ooze in this part of the Pacific ; the oxides of 

 iron and manganese, in the shape of minute grains, are seldom absent, and, 

 even when not present as grains, it is to them that the brown color of the 

 " fine washings " is due. 



1 Murray and Renard call particles exceeding 0.05 mm. in diameter " minerals." 



