REPORT ON THE DEEP-SEA DEPOSITS. 
405 
may be accounted for when we remember that the substance is not homogeneous, and is 
so fine in the grain that perfect separation is impossible even under the microscope. It 
may be added that, like other zeolites, these crystals are attacked by hydrochloric acid, 
leaving a siliceous skeleton. 
Geographical and Bathymetrical Distribution and Mineralogical Associations . — 
We have seen that phillipsite is present in nearly all the deposits collected by the 
Challenger in her voyage through the Central Pacific, from the Sandwich Islands to near 
the island of Juan Fernandez. It has also been detected in some of the deep-sea clays 
collected by the U.S.S. “ Tuscarora ” in the Central Pacific, and in the deposits collected 
by H.M.S. “Egeria” in the Central Indian Ocean. It always occurs in the deeper 
deposits, as will be seen by reference to the Tables of Chapter II., most abundantly 
in Ped Clays, more rarely in Radiolarian Oozes, and still more rarely in Globigerina 
Oozes. 
By reference to what has been said as to the distribution of basic volcanic glasses and 
basaltic lapilli, it will be seen that the distribution of these substances coincides with the 
distribution of the crystals of phillipsite. If the sounding tube has not demonstrated 
that the basin of the Pacific is covered at many points by flows of lava, it is because this 
apparatus cannot, any more than the dredge, penetrate below the surface of the sediment, 
and these superficial layers are always formed, as might be expected, of fragmental 
matters. But granted the accumulation of lapilli and volcanic ashes and sand that are 
found there, everything points to the conclusion that, beneath the deposits of mud, the 
bottom is constituted over considerable areas by veritable volcanic flows. Whether this 
supposition be correct or not, it is incontestable that, at those points far removed from 
continental land, and situated beyond the influence of transport by rivers, waves, tides, 
and currents, the elements most widely spread in the oceanic sediments are of volcanic 
nature, or result from the decomposition of eruptive products. It may be pointed 
out also that the volcanic matters predominating among these products of sub- 
marine eruption and scattered over this region of the ocean are from their nature 
essentially alterable, being mostly basic glasses. The basic nature, and at the same 
time vitreous condition, of these fragments is a certain index of alterability and of the 
facility with which sea-water can' attack and transform them. These points will be 
referred to presently, for they give the key to the mode of formation of zeolites in the 
deposits. 
Mode of Formation. — If we consider, in the first place, the subaerial rocks where 
zeolites are located, it will be seen that they are of the same nature as the volcanic 
fragments dredged from pelagic sediments, and that the conditions under which the 
zeolites are formed in both cases are analogous. It is a well-established fact that zeolites 
are never met with in fresh and unaltered rocks, neither are they ever observed as direct 
products of crystallisation in a magma nor as products of sublimation. They are specially 
