PLATE XXL 
Fig. 1. Section of nucleus of an elongated manganese nodule from Station 276 ; 2350 fathoms, South Pacific. 
This preparation offers an excellent example of the abundance and variety of volcanic products at 
the sea-bottom. The fragments of minerals and rocks have been enveloped by depositions of the 
peroxide of manganese, and form a veritable tufa composed of many species of rocks and minerals. 
Commencing at the top of the figure, there is a colourless crystal of plagioclase surrounded by 
altered vitreous matter, irregular colourless particles of volcanic glass, more or less vesicular, black 
and opaque fragments of volcanic rocks surrounded by a whitish zone of zeolites. Near the centre 
of the figure to the left is a particle of sideromelan, infiltrations of manganese, small volcanic 
fragments, basaltic lapilli wth pores filled with zeolites and an external zeolitic zone. To the right, 
embedded in the manganese, is a rather large black and opaque basaltic lapilli, in part surrounded 
by zeolites. Beneath this there is a rather large greenish fragment of pumice, and alongside of it 
a fragment of sideromelan. Towards the lower part of the figure there are again lapilli and 
fragments of zeolites surrounding or detached from the fragments of rocks. The yellowish mass 
in which all the fragments are embedded is composed of muddy matters more or less coloured with 
iron and manganese, and the whole surrounded by concretionary layers of the peroxide of manganese 
(magnified 37 diameters). 
Fig. 2. Section of volcanic tufa from Station 281 ; 2385 fathoms. South Pacific, the macroscopic appearance 
of which is represented on PI. IV. fig. 3. The figure shows two parts sharply marked off from 
each other : that to the right a more or less homogeneous Eed Clay, that to the left formed of an 
agglomeration of volcanic mineral particles representing a shower of volcanic ashes that had fallen 
upon the deposit. The whole has been surrounded by depositions of manganese, which have 
preserved the layers in their primitive position (see PI. IV. fig. 3). In the Eed Clay, near the 
lower part of the figure, a small manganese nodule is represented with a reddish centre ; the brown 
colour of the Red Clay passes in the layer of volcanic minerals to a greenish colour, due to the 
presence of numerous individuals of augite and hornblende. All these minerals are clastic, have a 
sharp fracture, and give the imjiression that they belong to a volcanic ash. The largest and most 
numerous are fragments of hornblende with a brown or greenish colour, and about 0*5 mm. in 
diameter ; augite is much less abundant, and the crystals are less deejily coloured. Felspars, 
especially fragments of plagioclase, can be observed, but they are generally altered and decomposed 
into a zeolitic substance. Finally, there are some little fragments of volcanic rocks, in which the 
jirincipal elements are microliths of augite, as well as fragments of magnetite, vitreous basaltic 
lafiilli, and peroxide of manganese (magnified 37 diameters). 
