REPOET ON THE DEEP-SEA DEPOSITS. 
393 
1 
1 
Portion Soluble in HCl. 
Portion Insoluble in HCl. 
1 station. I 
Depth. 
No. 
Loss on 
Ignition. 
SiO, 
ALO 3 
Fe^Oa 
MnOo 
CaCOj 
CaS 04 
Ca 32 P 04 
MgCOj 
Cu 
Total. 
SiO .4 
■^k03jFe203 
CaO 
MgO 
Total. 
14S 
1900 
74 
4-10 
6-00 
3-00 
5-80 
2-70 
16-07 
2-62 
49-57 
0-98 
tr. 
86-74 
8-40 
0-60 
0-16 
tr. 
9-16 ! 
Microscopic Characters. — The microscopic examination of thin sections of the 
phosphatic nodules shows that they present special peculiarities, depending on the 
nature of the deposit in which they have been formed. The phosphate of lime is the 
principal constituent, and presents the same characters in every one of the concretions 
examined, but the nodules differ in the nature and abundance of the heterogeneous 
particles cemented by the phosphate. These particles, whether of organic or mineral 
origin, are seen to be the same as those in the deposits containing the concretions ; for 
instance, the nodules from Station 142, where the deposit is a Green Sand, are princi- 
pally composed (to the extent of two-thirds) of glauconitic particles, quartz, and silicates 
(see PI. XX. fig. l), while in those from Station 143, Globigerina Ooze, the remains of 
Foraminifera predominate (see PI. XX. figs. 2-4). In the first case, where the aggrega- 
tions are formed of glauconitic and sandy particles, the phosphate pla 5 ^s simply the role 
of a cement interposed between the mineral grains. In the second case the phosphatic 
matter is more abundant, not only cementing the particles but penetrating through the 
cavities of the shells ; it fills up the spaces between the sections of the Foraminifera, 
and plays in a manner the role of a fundamental mass, pseudomorphosing, sometimes 
entirely, all the carbonate of lime of these organic remains. 
The phosphatic concretions from the above-mentioned Green Sand show under the 
microscope an agglutination of angular (rarely rounded) quartz grains, along with 
rounded glauconitic grains, all of which are abundant in the deposit ; there is neither 
pseudomorphism nor penetration of phosphate into the interior of the mineral particles ; 
the phosphate plays only a relatively subordinate part, binding together the mineral 
particles of the deposit (see PI. XX. fig. 1). It is distinguished by a brownish yellow 
tint, and is seen interposed between the minerals as a network of phosphatic matter. 
In the microscopic preparations isolated patches of phosphate, scarcely exceeding OT mm. 
in diameter, are occasionally to be seen ; one may observe upon these larger patches that 
the substance is concretionary ; they do not extinguish uniformly between crossed nicols, 
but spots with indefinite contours and vague tints of polarisation appear, like those pre- 
sented by very closely aggregated geodic minerals, chalcedony for example, or, better 
still, certain zeolites. 
The phosphatic concretions from the Globigerina Ooze in deeper water, 1900 
fathoms (see PI. XX. figs. 2-4), present considerable differences from those dredged 
(deep-sea deposits chall. exp. — 1891.) 50 
