THE DEEP SEA AND ITS CONTENTS. 329 



" As we have every reason to believe that this aggregation of 

 " the manganese is a very slow process, the occurrence of these 

 " teeth and bones, some embedded deeply, and some not at all, in 

 " the same surface-layers, argues strongly in favour of an extremely 

 "slow rate of deposition. On the other hand, the occurrence of 

 "sharks' teeth in shore deposits is extremely rare, and in the 

 "organic oozes slightly less so" — p. 495. 



This deposit of manganese seems, like that of the red clay, 

 traceable to a volcanic source : — ■ 



" Wherever we have pumice containing much magnetite, 

 " olivine, augite, or hornblende, and these apparently undergoing 

 " decomposition and alteration, or where we have great showers 

 " of volcanic ash, there also is manganese in the greatest abund- 

 "ance. The correspondence between the distribution of these 

 "two may therefore be regarded as very significant of the origin 

 "of the latter. Manganese is as frequent as iron in lavas ; and in 

 " magnetite and in some varieties of hornblende and augite it par- 

 " tially replaces peroxide of iron. It is therefore probable that the 

 " manganese, as we find it, is one of the secondary products arising 

 " from the decomposition of volcanic minerals, that decomposition 

 " being caused by the carbonic acid and oxygen of ocean-waters." 

 — Log- letters, p. 495. 



These deep-sea deposits of manganese differ in mineral structure 

 and composition from any of the known ores of that metal ; and 

 the conditions under which they are being formed constitute a 

 problem of very great interest, to which, as to other points of this 

 inquiry, a most distinguished Continental petrologist, the Abb^ 

 Renard, is now giving the most careful attention, with the full ex- 

 pectation of being able to throw great light upon the mode of 

 production of many minerals whose origin has been hitherto 

 unaccounted for. 



But there is yet another form of inorganic deposit whose 

 character is even more remarkable : — 



" In the midst of the clay from the bottom," says Professor 

 Geikie, " Mr. Murray found numerous minute spherical granules 

 "of native iron, which, as he suggests, are almost certainly of 

 meteoric origin — fragments of those falling stars which, coming to 

 us from planetary space, burst into fragments when they rush 



a 



