26 THE DEPTH AND MARINE DEPOSITS OF THE PACIFIC OCEAN. 



Olivine could be determined as such, with certainty, in a very few cases 

 only, owing mainly to the microscopic size of the particles ; it is, however, 

 very likely more widely distributed than appears from the descriptions of 

 the deposits, as it was often observed in the deposits of the 1899-1900 cruise. 



Magnetite is a widely-distributed mineral constituent, being rarely absent. 



Hematite is less frequently met with, though its occurrence is by no 

 means rare. 



Mica is relatively rare in these deep-sea deposits, and if present at all, is 

 always much decomposed, becoming opaque, and losing its birefringence. 



Very often mineral particles had to be put down as " products of decom- 

 position," when nothing pointed to the exact nature of the original 

 mineral. 



Quarts. By far the greater part of the deposits studied belong to the 

 pelagic class, so that quartz is rarely mentioned in the descriptions. Through 

 a defect in the labelling of the bottles practically all the samples of Blue 

 Muds, Green Muds, and Green Sands could not be localized, and had, there- 

 fore, to be left unstudied, a fact which brings down the degree of frequency of 

 quartz. It will be noticed that for the same reason other continental minerals, 

 such as tourmaline, zircon, and rutile, play no part in the descriptions, which 

 would not have been the case had these deposits been studied. 



Rock Fragments. The most frequent are fragments of rocks belonging to 

 basic lavas, augite-andesitcs. These are black, with conchoidal fracture, and 

 weather reddish-brown ; all the fragments observed are angular. 



From Station 4674, comparatively near the coast of Peru (lat. 12° 14' 

 S., long. 78° 43' W.), some very large pieces of rock were dredged. They 

 consist of angular pieces, some of them over a foot in length, of hard, com- 

 pact, slightly argillaceous litnestone, greenish-gray in color, containing in 

 some places numerous examples of a Foraminifer belonging to the Textula- 

 ridae, probably BoUvina. 



At Station 4622 (lat. 6° 21' N., long. 81° 44' W.) a peculiar manga- 

 nese nodule was dredged containing a nucleus made up of a white, hard, 

 granular, silicified limestone, flat and angular, and doubtless of continental 

 origin. 



Secondary Minerals. Of minerals formed in situ the most frequently rep- 

 resented is glauconite, but as already stated, the deposits in which it is 

 formed were badly labelled, and were not studied. We shall not ndd any 

 more to the subject of glauconite, as part of the material on which our study 



