24 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



With the exception of three samples ( from Stations 4649, 4666, 4672), 

 collected very near the limit of the Blue Mud, the " Albatross " Red Clay- 

 shows all the typical characters of the deposit as regards its mineral con- 

 stituents. The exceptions alluded to are clays in which quartz and 

 glauconite were detected ; on account of these minerals the deposit might 

 perhaps in two cases have been called Blue Mud, but the total amount 

 of minerals having been estimated as traces, it may also be called Red 

 Clay, as it passes seawards into undoubted Red Clay, and there is no 

 Globigerina Ooze marking the limit between these two deposits. The third 

 sample partakes much more of the nature of Red Clay than of that of 

 Blue Mud, as among the minerals manganese grains and volcanic glass are 

 conspicuous (Station 4666). 



Manganese nodules were present in six of the samples studied, and a 

 greater number would, no doubt, be at hand, were it not for the fact that 

 at many stations soundings alone were taken ; trawling would almost cer- 

 tainly have shown the presence of nodules at all the stations, as manganese 

 is always present in the form of grains. The nodules of Station 4658 

 (lat. 8° 29' S., long. 85° 35' W.), in 2370 fathoms, must rank among the 

 finest ever dredged ; they are of high specific gravity, very free from 

 foreign admixture, their shape is remarkably constant, and most of them 

 attain a very large size indeed. 



The minerals that could be accurately determined, and that without any 

 doubt as to their true nature, were not very numerous, the same species 

 being generally represented in different stations with its usual characters. 



Augite. Of clastic minerals the most frequently met with is a very pale 

 brown, nearly colorless augite, generally in fragments, entire crystals being 

 unusual. 



Plagioclase. Next in order of abundance comes plagioclase, which, nearly 

 every time it exhibits the necessary optical properties required for accurate 

 determination, turns out to be a labradorite. For this determination use 

 was made as much as possible of sections of definite orientation, preferably 

 of those perpendicular to the acute or the obtuse bisectrix, and the results 

 were calculated from the data given by Mr. Michel Levy in his treatise on 

 the determination of felspars. Very often, however, when the crystals were 

 too small, as in the case of microlites, the determination had to be based on the 

 measure of the value of the angle of extinction on lamellae perpendicular to 



