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 Lévy 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 lamelle perpendicular to 
