REPOKT ON THE DEEP-SEA DEPOSITS. 
311 
These observations relative to the time at which the eruption of these lapilli took 
place are also applicable in a certain way to all the volcanic rocks found in a frag- 
mentary condition in pelagic deposits. Some of these lapilli are allied in fact by 
insensible transitions to the vitreous type described above. Such, for instance, are 
fragments of felspathic basalt with a highly developed vitreous base ; they are associated 
with the basic glasses, and probably belong to the same age. 
In other cases some fragments of basalt, of augite-andesite, of trachyte, appear to be 
the products of eruptions of a more recent date, for, although there may be among them 
fragments coated with thick layers of manganese, there are others which have only a 
thin coating of that substance, and it seems legitimate to conclude that the greater or 
less thickness of the deposits of manganese indicates in a manner the relative length of 
time that the fragments have lain on the bottom of the sea. The relative age indicated 
by these different layers of manganese, which surround volcanic fragments and remains 
of organisms, will be fully referred to when treating of manganese nodules. 
In the descriptions of the Challenger specimens, in Chapter II, , palagonitic materials 
are mentioned twenty times in Red Clay, four times in Radiolarian Ooze, once in Diatom 
Ooze, ten times in Globigerina Ooze, three times in Blue Mud, four times in Volcanic 
Mud, and twice in Volcanic Sand. It will thus be observed that it is especially in the 
pelagic deposits, and among these in the red clay areas, that the palagonitic substances 
were most frequently observed. 
Basaltic and other lapilli . — We may be brief with the description of basaltic 
lapilli, which are often found associated with the lapilli of basic glass, and form along 
with them centres of manganese nodules. Some basaltic fragments are less angular than 
those found in the manganese nodules, and might even be taken for rolled pebbles, from 
their smooth surface and rounded exterior, and these, from the thin coating of manganese 
with which they are covered, have not, in all probability, the same origin as those 
forming the nuclei of nodules. Basaltic fragments are as frequent in the deposits as the 
palagonitic lapilli, but their determination is not always so easy, especially when they are 
small and altered, for their characters are much less sharply marked than those of the 
palagonitic materials. In consequence we have often distinguished the basaltic frag- 
ments, in the Tables of Chapter II., under the vague names of scoriae, lapilli, and glassy 
volcanic particles, it being impossible to be more specific. However, many of the little 
fragments thus indicated belong undoubtedly to basalts, generally to basalts with a 
vitreous base, to felspathic basalts ; basalts with leucite or nepheline cannot be said with 
certainty to have been observed. 
Basaltic fragments are found under the same conditions as the basic glasses, 
their dimensions are the same, and they are specially numerous in the same stations 
where the palagonitic tufas were dredged. They are distinguished from the vitreous 
lapilli by their mineralogical composition, which is that of ordinary basalts — olivine. 
