SEA-WATER AS A SOURCE OF MINERALS. 399 



Singapore, except that the large pores are lined with oxide of iron. 

 Boron is found in the rock salt of Strassfurth in Germany, and this 

 is presumably of marine origin, while the plant Zostera marina 

 contains much Boracic acid. Silver, though difficult to detect in sea 

 water, is yet so abundant in the coral Pocillipora alcicornis, that one 

 cubic foot of coral yields about half a grain of silver. Copper is 

 frequently found in the lime salts of sea animals and plants, and in 

 the coral Pocillipora there is six times more copper than silver ; the 

 ash of Fucus vesiculosus contains copper. Lead is more abundant 

 in shells and ashes of sea plants than even copper. Pocillipora 

 alcicornis contains eight times as much lead as silver ; lead also 

 occurs in the Fucus vesiculosus. Zinc is found in the ashes of sea 

 plants, such as Fucus vesiculosus, and in Zostera marina it occurs to 

 the extent of i part in 3000. As the mineral Blende, it is common 

 in the Ammonites cordatus from the Oxford clay of St. Ives. 

 Cobalt occurs in Zostera marina, in the large cup sponge from 

 Singapore, and in fossil sponges from the chalk. Nickel, in minute 

 quantities, seems to occur with Cobalt. Iron in great quantity is 

 found in the ashes of sea-weeds and lime-salts of sea animals. 

 Manganese forms nearly 4 per cent, of the ash of Zostera marina. 

 Aluminium is more abundant than any metal except iron and per- 

 haps manganese. Magnesium usually forms i per cent, of shells, 

 though it forms 13 J per cent, of the shell of Serpula filigramma. 

 Calcium, as carbonate of lime, forms '003 of sea water, and is 

 abundant in all shells, &c. Strontium is found in the ashes of 

 Fucoids. Baryta is common in sea animals and abundant in the 

 ashes of sea plants. And there are the universally diffused substances 

 Sodium and Potassium. 



These substances being thus diffused in nature and accumulated 

 by organisms, the strata become charged with them ; and hence, 

 when metamorphic changes raise the temperature and dissolve the 

 whole substance of the strata, with the production of multitudes of 

 fractures, joints, and faults, it is easy to conceive the steps of change 

 by which these minute particles become dissolved, extruded by crystal- 

 lisation of the rock, and deposited in veins. 



DaubreVs Views on the Origin of Ores. Mr. Daubre'e urges l 

 that the ores which occur as sulphides are all to be attributed to the 

 action of sulphurous waters upon metallic substances. Thus Roman 

 coins buried in mud in the warm spring at Bourboune-les-Bains are 

 more or less converted into copper pyrites and other cupric sulphides. 

 Lead pipes have yielded a coating of galena, which M. Daubree attri- 

 butes to the decomposition of phosgenite under the reducing influence 

 of organic matter. Iron pyrites appear to be frequently formed under 

 the influence of decaying organic matter, especially plants, but it 

 assumes a more characteristic form in the waters of sulphurous springs. 

 In Iceland it is developed by the action of sulphuretted hydrogen on 

 the iron in basaltic rocks. 



Difference between Dykes and Veins. Though in some instances 

 1 " Geologic Experimentale," 1879. 



