THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 27 



of this mineral was based ^ came from the eastern shores of the Pacific in the 

 neighborhood of the track of the " Albatross." 



The ooddes of iron and manganese are widely distributed in the pelagic 

 deposits, either as grains or as nodules. There is hardly a Red Clay or a 

 Globigerina Ooze that does not contain manganese grains, or, at least, 

 minute particles diffused in the " fine washings." The grains average 0.1 mm. 

 in diameter, and have generally a botryoidal shape and shining surface ; the 

 minute particles found in the " fine washings " have no sharply defined out- 

 lines, and appear to be mixed with more or less clayey matter, giving them 

 a flocculent appearance. 



Phillipsite is of frequent occurrence and has been observed in Globigerina 

 Ooze as well as in Red Clay, but not in such large amount as is the case with 

 some of the Red Clays dredged further south by the " Challenger." Isolated 

 crystals are much m.ore frequent than clusters ; their breadth is relatively 

 larger than in the case of those found by the " Challenger," the proportion 

 of breadth to length being generally from 1 to 3 to 1 to 4. As it often 

 happened that only little material was available, it is quite possible that 

 phillipsite may have escaped observation more than once, and, therefore, may 

 be more abundantly distributed than it appears to be from the descriptions. 



Methods used for Determination. Examination in reflected light with the 

 binocular microscope was always made of the mineral particles as they 

 stood after removal of the carbonate of calcium and the washing away of 

 the finer material. This examination gives indications as to the weathering 

 of the minerals, and as to their mutual relations, that is, a particle of mag- 

 netite, for instance, may be quite free, or, on the other hand, firmly attached 

 to some other mineral. 



After this preliminary examination the particles are measured with a 

 graduated ocular micrometer, and then, if sufficiently thin, directly exam- 

 ined under the mineralogical microscope. For all purposes one can dispense 

 with actual slides mounted in balsam ; if the particles are too thick, they are 

 ground in an agate mortar to the requisite thinness ; the diameter will, of 

 coui'se, correspondingly decrease, but with a high power and an ocular fur- 

 nished with an iris diaphragm, the figures of interference in convergent light 

 can still easily be observed. This method saves much of the time that would 

 be required in order to make thin slices, and allows the studying of different 



1 See Collet et Lee, " Kecherohes sur la Glaucouie." Proc. Roy. Soc. Edin., Vol. XXVI., p. 238, 

 1906. 



