relations Bs the Metamorphic Rocks. pe 
carbonates of the latter bases. Soils in like manner remove, 
pow infiltrating waters, ammonia, ‘ike nphoaphans and silicic 
acids, the bases which were in combination with these being 
converted into carbonates. The drainage water of soils, like 
are precisely those which are removed from it by growing plants. 
hese, by their decomposition under igo facil eta yield 
their mineral matters again to the soil; but, when decay takes 
place in water, these elements vets dissolved, ae hence the 
waters from peat bogs and marshes contain large amounts of 
potash and of silica in solution, which are carried to the sea, 
there to be separated—the silica by protophytes, and the potash 
by alge, which latter, decaying on the shore, or in the ooze at 
the bottom, restore the alkali to the earth, The conditions un- 
der which the vegetation of the coal formation grew and was 
fee of pen similar to those of peat, the soils became ex- 
Se ie 
is withdrawn from the terrestrial circulation; and it is evident 
that the proportion of this element diffused in the more recent 
sediments must be much less than in those of ancient times. The 
precipitated in this insoluble form the heavy metals, were — 
- and zine, which, with iron, appear to have been in solution 
the waters of earl times, but are now by this means sais ts 
stracted from ae circulation, and accumulated in beds and fahl- 
nds, or by a subsequent process have been redisso. lved and de- 
ited in veins. All analogies lead us to the conclusion that 
a primeval condition of the metals, and of sulphur, was, like 
that of carbon, one of oxydation, and that vegetable life has 
been the sole medium of their reduction. 
The source of the carbonates of lime and magnesia in sediment- 
ary strata is two-fold: first, the decomposition of silicates contain- 
Am. Jour. Sct.—Srconp Serres, Vou. XXXVI, No. 107.—Szpt., 1863, 
28 
