NARRATIVE OF THE CRUISE. 
813 
quantity of substance available, only a qualitative analysis could be made, which showed 
the presence in them of silica, magnesia, and iron. 
“ These remarks have been limited to these succinct details, but it is believed 
that enough has been said to show that these spherules in their essential characters 
are related to the chonclres of meteorites, and have the same mode of formation. 
In conclusion, it may be stated that when the coating of manganese depositions, which 
surround Sharks’ teeth, earbones of Cetaceans, and other nuclei, is broken off and pounded 
in a mortar to fine dust, and the magnetic particles then extracted by means of a magnet, 
these latter are found to be composed of silicate spherules, spherules with a metallic 
centre, and magnetic iron, in all respects similar to those found in the deposits in which 
the nodules were embedded.” 
Mr. Murray 1 has pointed out the large part played by volcanic debris and the products 
arising from its decomposition in the formation of deep-sea deposits, and the microscopic 
characters of these materials have been described by Messrs. Murray and Renard in more 
recent papers. 2 Since these volcanic materials were especially abundant in the deep 
water of the Central Pacific, and as they, owing to the slow accumulation of the deposits, 
have been long subjected to hydrochemical action, the chief peculiarities of the rocks and 
minerals brought up by the dredge in this region may be pointed out. At two Stations 
near the 38th parallel of south latitude, one or two fragments of granite, gneiss, and 
arkose were obtained, which fact seems to show that a stray iceberg may occasionally reach 
this low latitude. With the above exception all the. rocks and minerals dredged from 
the Central Pacific were of volcanic origin. Pumice was present in all the dredgings, but 
the most abundant fragments belonged to the family of the basalts, and the majority of 
these belonged to the vitreous series of those basic rocks. Rarely some specimens 
contained hornblende and sanidine. The basaltic, generally vitreous, rocks are represented 
by fragments rarely exceeding a few centimetres in maximum diameter. From their 
form, their association with volcanic ash, and their lithological constitution, they cannot 
be considered as derived from lava flows spread over the sea bottom, but rather as frag- 
mentary materials such as lapilli and volcanic ash, the accumulation of which at some 
spots on the floor of the Pacific appears to constitute submarine tuffs, which by their 
mode of origin probably resemble in many respects that attributed by Murchison and 
Ramsay to certain igneous beds regularly intercalated among the Palaeozoic formations of 
the British Islands. 
The fragments, are usually incrusted with and infiltrated by peroxide of manganese, 
1 On the Distribution of Volcanic Debris over the Floor of the Ocean, &c., Proc. Roy. Soc. Edin., vol. ix. 
pp. 247-261, 1877. 
2 On the Nomenclature, Origin, and Distribution of Deep-Sea Deposits, Ibid., vol. xii. pp. 495-529, 1884 ; On 
the Microscopical Characters of Volcanic Ashes and Cosmic Dust, and their Distribution in Deep-Sea Deposits, Ibid., 
pp. 474-495, 1884. 
