316 
THE VOYAGE OF H.M.S. CHALLENGER: 
between the ash and Red Clay, the left of the figure representing the ash and the 
right the Red Clay. In the volcanic ash all the minerals are clastic, irregularly dis- 
posed, with almost no interposition of clay. This accumulation has a greenish tint 
due to the presence of a large number of fragments of augite, hornblende, delessite or 
chloritic substance. The outlines of almost aU the crystals are blunted as if broken. 
Hornblende is represented by fragments of a brownish or dark greenish colour, with the 
characteristic cleavages, strongly pleochroic. The crystals of augite are greenish or 
brown-violet ; very often augite is present in the form of aggregated microliths 
surrounded by delessite. There is also a large number of sections of felspar belonging 
to plagioclase or sanidine ; they are colourless, more or less irregular, and generally 
transformed into zeolitic matter. Moreover, there are in this ash rather small lapilli, 
principally formed of an aggregation of green microliths of augite and small fragments 
of basalts, or of highly-altered basic glass. Finally, there are numerous grains of 
magnetite, of manganese, and of olivine transformed into hematite. All these mineral 
particles are cemented by colourless zeolitic substances. 
The general appearance of these particles under the microscope is further represented 
in some of the lithographic plates at the end of the volume. Plate XXVI. fig. 2 shows 
numerous minute vitreous splinters transformed into palagonite and coloured by manga- 
nese and iron, along with augite, plagioclase, magnetite, from a Red Clay, Station 282, 2450 
fathoms. South Pacific. Fig. 3 of the same plate represents the mineral particles of a 
Red Clay from the South Pacific, off the coast of Australia, Station 165a, 2600 fathoms. 
There are numerous angular fragments of volcanic glass with elongated pores and ragged 
outlines among the particles of felspar, hornblende, grains of manganese, and minute 
rounded particles of quartz. The rounded fragments of quartz coloured with limonite, 
represented in this figure, are evidently wind-borne particles from the continent of 
Australia. PI. XXVII. fig. 2 represents the mineral fragments and fine washings in a 
Red Clay from the South Pacific, Station 178, 2650 fathoms. Besides the crystals of 
felsj)ar and augite there are numerous vitreous, colourless, volcanic particles with 
elongated pores, and in addition to these a very large number of extremely minute 
[)articles of the same nature, which make up the principal part of what we denomi- 
nate in this w’ork “ fine washing.s.” These smaller microscopic particles are more or 
less angular, forming an impalpable powder, and it will be seen that they cover the 
field of the figure between the larger mineral particles. PI. XXVII. fig. 3 shows again 
abundance of vitreous particles of pumice, along with volcanie minerals, from a Red Clay 
in the North Pacific, Station 240, 2900 fathoms. As in all the preceding residues, the 
mineral jjarticles are angular ; the vitreous particles are sharply characterised by their 
ragged outlines and their strueture, and among them are some vitreous grains trans- 
formed into palagonite. PI. XXVH. fig. 4 presents once more an abundance of volcanic 
particles from a Red Clay, South Pacific, Station 294, 2270 fathoms. The vitreous 
