WORLD-MAKING I? 



we infer that it was laid down layer by layer in the manner 

 of aqueous deposits. On the other hand, its chemical com- 

 position is quite different from that of the muds, sands and 

 gravels usually deposited from water. Their special charac- 

 ters are caused by the fact that they have resulted from the 

 slow decay of rocks like these gneisses, under the operation of 

 carbon dioxide and water, whereby the alkaline matter and 

 the more soluble part of the silica have been washed away, 

 leaving a residue mainly silicious and aluminous. Such 

 more modern rocks tell of dry land subjected to atmospheric 

 decay and ram-wash. If they have any direct relation to the 

 old gneisses, they are their grandchildren, not their parents. 

 On the contrary, the oldest gneisses show no pebbles or sand 

 or limestone nothing to indicate that there was then any 

 land undergoing atmospheric waste, or shores with sand 

 and gravel. For all that we know to the contrary, these 

 old gneisses may have been deposited in a shoreless sea, hold- 

 ing in solution or suspension merely what it could derive 

 from a submerged crust recently cooled from a state of fusion, 

 still thin, and exuding here and there through its fissures 

 heated waters and volcanic products. This, it may be observed 

 here, is just what we have a right to expect, if the earth was 

 once a heated or fluid mass, and if our oldest Laurentian rocks 

 consist of the first beds or layers deposited upon it, perhaps by 

 a heated ocean. It has been well said that " the secret of the 

 earth's hot youth has been well kept." But with the help of 

 physical science we can guess at an originally heat-liquefied 

 ball with denser matter at its centre, lighter and oxidised 

 matter at its surface. We can imagine a scum or crust form- 

 ing at the surface ; and from what we know of the earth's in- 

 terior, nothing is more likely to have constituted that slaggy 



1 Carbon dioxide, the great agent in the decay of silicious rocks, must 

 then have constituted a very much larger part of the atmosphere than at 

 present. 



