404 
THE VOYAGE OF H.M.S. CHALLENGER. 
edge c/6. They advance more or less regularly following the radii, growing gradually larger 
as they approach the periphery ; this structure, however, is not quite what is denominated 
tibro-radiate. The individuality of each crystal is too well marked ; properly speaking, it 
is a radiate structure. The section cuts some of the crystals more or less parallel to the axis 
of elongation, and the extremity is then seen to be terminated by the faces mjm. Zones 
of growth may be observed upon these microliths, indicated by inclusions of the limonitic 
and manganiferous mud ; in many cases these zones do not present a well-marked direc- 
tion, but sometimes the inclusions are arranged and disposed en chevron, which might 
answer to the arrangement of the hemitropic lamellae observed upon the face 6 of crystals 
of phillipsite. Even in these pretty large crystals of the spheroliths it is very difficult to 
discern the optical properties exactly, and this difficulty is increased by reason of the 
wedge-shaped form affected by each of the individuals ; in the spheroliths the properties 
of the individual crystals, as in the case of a twin, lose all regularity. PI. XXII. 
fig. 2 shows one of the spherules cut nearer to the surface, consequently the section 
cuts the radial crystals near their external extremity. Sometimes the form of the 
sections is a parallelogram more or less elongated, or approaches to a square, 
according as they are cut more or less normally to the edge c/6 ; this is what the 
crystals of phillipsite should give when cut across in such a section. Sometimes 
sections with re-entrant angles are also observed, and are the traces of crossed twins ; 
two or three such sections are seen in the spherule figured, at the upper right-hand 
side of the figure. 
Chemical Composition . — From the physical characters just described, it is evident 
that these crystals belong to the species phillipsite, and the results of the following analyses 
confirm this determination. The material chosen for the analyses was as pure as it could 
be obtained by decantation, or by the aid of dense liquids, without being cleaned with 
acid.‘ 
Station. 
Depth. 
No. 
Loss 
on igni- 
tion. 
SiOj 
AI 2 O 3 
FegOg 
MnO 
CaO 
MgO 
KgO 
Na 20 
H 2 O 
Total 
275 
2610 
89 
7-59 
47-60 
17-09 
5-92 
0-43 
3-20 
1-24 
4-81 
4-08 
9-15 
101-11 
275 
2610 
90 
7-35 
49-88 
16-52 
5-54 
0-44 
1-38 
1-20 
5-10 
4-59 
9-33 
101-33 
275 
2610 
91 
9-47 
48-70 
17-58 
6-17 
1-70 
1-02 
4-83 
3-75 
7-95 
101-17 
The presence of iron and manganese must be placed against the coatings and inclusions 
of the crystals. Apart from these foreign matters, the composition shown by the 
analyses corresponds closely with the average composition of phillipsite, except in the 
case of the alumina, the percentage of which is rather below the average ; this deviation 
* In Ajijtcnflix HI. will he found three additional Analyses (Nos. 20, 21, and 92), which were made from impure 
material or are incomplete, and need not la: specially referred to here. 
