328 
THE VOYAGE OF H.M.S. CHALLENGER. 
nodule from the South Pacific, Station 285, 2375 fathoms. This grain is perfectly 
spherical, and is drawn so that the little depression is on the opposite side from the 
observer ; it shows the aspect presented by these granules in reflected light under the 
microscope. The surface with metallic lustre is not perfectly smooth, but appears as if 
scattered with a large number of little asperities or pores. Fig. 4 represents a spherule 
from the same station identical in form and aspect with the preceding, but showing the 
cupule which is seldom absent in these magnetic globules. This cupule, it will be seen, 
is a circular depression attaining sometimes a diameter equal to half of that of the 
spherule, and appears to be characteristic of these granules ; we shall presently 
endeavour to interpret its formation. The spherule represented in fig. 6, from the South 
Pacific, Station 276, 2350 fathoms, is much the same as the two others just described, 
but is interesting, showing, as it does, the manner in which it reposed at the bottom of 
the sea, being surrounded and fixed among little crystals of phillipsite, found in abun- 
dance at the bottom of the sea in certain regions. In some cases, which have not been 
figured, two spherules are coupled together, the one much smaller than the other, 
resembling two drops of molten matter soldered together in solidifying. 
Turning now to their internal structure, the nature of the nucleus furnishes the 
principal characteristic uniting these spherules to the meteorites. The superficial crust 
may be easily detached, by breaking one of the spherules, and is usually found to cover 
a nucleus of a metallic nature, as shown in fig. 8, representing a spherule from the South 
Pacific, Station 285, 2375 fathoms, in which a part of the outer coating of magnetite has 
been removed. In this spherule, which resembles in every respect those previously 
referred to, the nucleus is seen with its metallic lustre, grey colour like steel, and slightly 
granular. Oxidation has apparently only taken place at the periphery, where magnetic 
oxide has been formed, while the centre, protected from further oxidation by this coating 
of magnetite, has remained in the state of native iron or alloy of iron. Fig. 5 shows a 
similar spherule from the South Pacific, Station 276, 2350 fathoms, in which the thin 
shell of magnetic iron has likewise been partially removed to show the metallic nucleus. 
This nucleus behaves like iron, being malleable and taking the impress of the pestle ; 
treated under the microscope with an acid solution of sulphate of copper it is at once 
covered by a coating of copper. Fig. 9 represents a nucleus from the same station 
(Station 276), treated in a similar way, showing the coppery coating; it has become 
di.scoid under the pressure of the pestle and bears its impress. In some cases the nucleus, 
though malleable, does not present this reaction with sulphate of copper solution. Fig. 7 
reprc.sents such a nucleus, from the same station (Station 276), wdiich, though treated 
with the copper solution, has retained its original grey steel-like colour. This nucleus, 
unaffected by the copper, may be schreibersite (NijFe^P), or an alloy of iron, cobalt, and 
iii<-kel, {IS in certain meteorites in which the last two metals are present in consideralfie 
quantities. It is known, in fact, that cert{iin meteoric irons are insensible to the reaction 
