THE VOYAGE OF H.M.S. CHALLENGER. 
\iOS 
The brecciaform character of these eruptive products is clearly represented by some 
of the figures on the accompanyiug plates, where these lapilli are shown as they appear 
aggregated in some of the deposits. The nuclei of the nodules of manganese from 
Station 276 and other stations in the South Pacific are in some instances crowded with 
splinters of basic glasses or palagonite. These fragments do not always belong to 
the same types ; they present differences of stiucture and of mineralogical composition, 
such as might be found in volcanic tufas, but they have not the homogeneity of an 
accumulation of fragments derived from the trituration of a lava-flow. It is sufficient to 
cast a glance at PI. XXL fig. 1 to be convinced of the correctness of the above observa- 
tions ; this figure represents a thin section cut from the interior of an elongated man- 
ganese nodule, in which numerous fragments of basic glass, of felspathic basalt, and 
volcanic minerals may be observed, all presenting the character of lapilli. Not only the 
essentially vitreous nature, the mineralogical composition, and the structure, but also the 
form of the splinters — angular and without trace of wear and tear — all prove that these 
particles have not been submitted to the mechanical action of water. Commencing at 
the top of the figure there are large crystals of plagioclase surrounded by vitreous matter 
or by microliths ; descending towards the centre of the figure is a large number of small 
angular fragments of basic glass, scoriaceous, yellowish, transparent, coated by zeolites, or 
black and opaque, and containing lamellae of plagioclase ; in the manganese to the right 
near the centre are small zeolitic crystals, and lower down is a large lapilli of black 
opaque volcanic glass ; next to it is a section of very vesicular pumice, opposite which is 
a fragment of basic glass ; near the lower part of the figure are accumulated plagioclases 
and splinters of volcanic glass more or less surrounded by zeolitic zones. In fact the 
aggregation of about fifty volcanic fragments in this nodule affords a very striking and 
t}q)ical example of the tufaceous character of these fragments of basic rocks as found at 
the bottom of the sea. This is also clearly shown by the palagonitic fragments 
enclosed in a manganese nodule, represented in PI. XVIII. fig. 1. It seems necessary, 
then, to conclude that the angular form is original and due to the mode of projection, 
these splinters of basic glass being thrown out in the form in which they are now 
found. It does not seem possible to admit that they are clastic in the ordinary sense 
of the word, for there is no reason for believing that in the depths from which they 
were collected the mechanical movements of the sea are capable of producing the accu- 
mulation and fragmentation of these splinters. Still another argument in favour of 
the view as to tlie origin of these fragments here advocated, is their association with 
numerous volcanic fragments of very small dimensions ; these latter are undoubtedly 
ashes, and it is neces.sary to admit the same mode of formation for them as for the 
larger fragments. 
Tlie cementation of these minute particles and lapilli by zeolites presents still 
another point of resemblance with palagonitic tufas. Not only have the zeolites 
