MACKIE THE GEOLOGY OF THE SEA. 



247 



silicates or felspars must liave played, as they still contiime to do, in 

 the chemistry of the sea. Hence the analyses and stndy of the per- 

 colating waters of the remaining areas of those ancient gneissic and 

 bottom-most sedimentary rocks mnst be one of the chief points in the 

 elucidation of our question, Was the sea always salt ? 



Another point of interest still remains, namely the study of the 

 present constituents of those old primeval rocks. If water dissolves 

 out certain substances from them, and the dissolution has been going 

 on for ages, it follows there must be a diminished quantity or absence 

 of certain soluble materials, and by consequence a proportionate pre- 

 dominence of insoluble, in the residue of which their present consti- 

 tution consists. 



The yellow corn waves its golden seed-bearing spikes in the 

 summer's breeze, and the harvest is reaped and stored into barns ; 

 but the farmer in the inclement days of winter spreads his fields with 

 manure, and ploughs and fmTows the soil, opening and turning it 

 up to the rain, the frost, and the air. 



And why ? To replace that which the corn has extracted, and 

 that the elements in their chemistry and powers may manipulate 

 fresh substances required for another crop. 



If we analysed the soil before the crop was grown, would it 

 be the same as after the crop was reaped ? Assuredly not, so if we 

 analyse the ancient rocks after ages of loss of certain original 

 ingTedients by the incessant dissolving action of percolating springs, 

 they would shew, as we have remarked, a poverty of some sub- 

 stances and a superabundance of others. Thus it is that while 

 we find the potash small in quantity in alkaline and saline waters, we 

 find it locked up in superabundant proportion in orthoclase and other 

 indissoluble forms in the constituent rocks of the earth's crust, while 

 soda, which we find abundant in alkaline and saline springs, is 

 observed gradually to diminish in quantity from the oldest granitic 

 and gTieissic rocks through their regenerated materials in the paleo- 

 zoic, secondary, tertiary, and recent eras, becoming less and less as 

 their periods of formation approach our own. : 



These conditions and results are readily and mutually explained 

 by the soluble substances found in mineral-bearing waters, and by the 

 actual constitution of the residue of the rock-mass. So the double- 



