246 



THE GEOLOGIST. 



sand-running to modem chronometers, lever- watches, and to tlie 

 delicate hijoux not larger tlian sliillings, manufactured at this day in 

 the famous old city of Geneva. 



So it is in investigating any one subject of geological history. So 

 mingled do we find it, so associated with other topics, as to be only 

 unriddled or comprehended by very extensive and very different 

 investigations. 



Look at that little rill issuing from the base of the chalk-downs, 

 and trickling onwards to the green meadows, That rill has filtered 

 through the chalk-rock, and few of us need a chemist to tell us 

 that the crystal-looking water contains a large amount of chalky 

 matter, for the evidence is plain in the incrustation of the bits of 

 sticks and other objects in its rippling course ; but still we want the 

 chemist's art to know that it is carbonic acid gas which enables the 

 water to dissolve out that chalky matter from the solid hills, to hold 

 it in solution, and that it is when the water liberates some portion 

 of that gas into the atmosphere that the water becomes incapable of 

 sustaining the whole of its chalky load a.nd the encrusting sediment 

 is deposited. 



So other waters and other springs issuing from other rocks, and 

 in other countries, contain other materials in solution according to 

 the nature of the substance they permeate, as witness the natron- 

 lakes of Egypt, the carbonate of soda springs of Carlsbad and Yichy, 

 the siliceous waters of the geysers, and the ordinary calybeate and 

 medicinal springs. 



ISTow for ages upon ages throughout all time since the dry land 

 has peered above the sea has the percolation of water and the issuing 

 of springs taken place ; from the hour when the first rain-di'ops fell 

 unto the present have the dissolving and re-combining, the undoing 

 and re-forming processes been going on. What has been taken from 

 one place has been carried to another. What has been taken from 

 the land has been given to the sea. 



When we consider all the vast amount of clays mingled with the 

 other strata in the earth's crust has been originall}' derived from the 

 decomposition of the felspathic mmerals of the old gneissic rocks, we 

 }Hn*ccive by comparison at once the importance of the part which the 

 alkaline carbonates formed in the decomposition of the alkaliferous 



