396 Review of the Progress of 
organization ; plants by solar force convert water and carbonic 
acid into hydrocarbonaceous substances, from whence bitumens, 
coal, anthracite and plumbago, and it is the action of organic 
matter which reduces sulphates, giving rise to metallic sulphu- 
rets and sulphur. In like manner it is by the action of dissolved 
organic matters that oxyd of iron is epee reduced and dis- 
solved from great masses of sediments, to be subsequently accu- 
mulated in beds of iron ore. We ai Bee in the Laurentian series - 
beds and veins of metallic sulphurets, precisely as in more recent 
ese and the extensive e beds of iron ore hundreds of feet 
tian limestone which cannot be distinguished from the silicified 
specimens of Stromatopora rugosa found in the Lower Silurian 
rocks. They consist of concentric layers made up of crystalline 
grains of white pyroxene in one case and of serpentine in an- 
other, the first imbedded in limestone and the second in dolo- 
mite; we may well suppose that the result of metamorphism 
be uld be to convert silicified fossils into silicates of lime and 
agnesia. ‘The nodules of phosphate of lime in some beds of 
Gpoe Lingula, Orbieula, Conulari fpr the shells and 
tubes of which we have long since sane to be similar in com- 
oes to the bones of vertebrates.* So far therefore from 
ooking upon the base of the Silurian as marking the dawn of. 
‘life upon our planet, we see abundant reasons for. ee posing that 
organisms, probably as varied and abundant as those of the 
* Logan and Hunt, Amer. Jour. Sci. [2], xvii, 235, 
a ee 
