1898-99. | On some Geological Agents. 23 
I call them, there is an enormous annual amount of geological 
work done by this one river. 
Rivers also hold much matter in solution, such as carbonate 
of lime, sulphate of lime, &c. The Thames—a river flowing 
through and draining a calcareous country—carries an esti- 
mated quantity of 600,000 tons of carbonate of lime past 
Kingston annually; and as showing the difference in the 
quantity of matter carried by a river in suspension and in 
solution, I will mention the Danube, with nearly 68,000,000 
tons in suspension, and 22,521,000 in solution. What is the 
weight of the material rolled along the bottom of a river 
in the form of gravel and stones cannot be estimated with 
any approach to certainty. 
Now for one or two illustrations of the chemical power of 
water. Rain in falling through the atmosphere absorbs or 
dissolves carbonic acid gas—the carbonic dioxide of the 
chemist. Decaying vegetation supplies this gas too. As 
this rain-water, with its supply of carbonic acid, flows over 
the land or descends into the earth, it dissolves the carbonate 
out of the limestone, leaving only the impure matter, often 
called rotten-stone, which is chiefly composed of silicate of 
alumina, iron, &c. The dissolved carbonate finds its way 
into springs and streams, sometimes deposited as calcareous 
tuff or tufa, as at Starleyburn in Fife, and frequently as 
an incrustation in our kettles and boilers. Where the lime- 
stone is very pure, almost the whole of it is dissolved by rain 
or running water. 
But water charged with carbonic acid, &c., does not confine 
its solvent action to limestone alone. It attacks the lime and 
potash felspars in rocks, and breaks up their chemical union 
with other substances. Here is a specimen of granite, where 
you can see that the felspar has been eaten away, and the 
quartz particles left standing out in relief. Iron is also dis- 
solved out of rocks, as you can see by the red deposits of 
some springs. I have here some specimens of bog-iron ore, 
probably dissolved out of the West Kip, and re-deposited 
some inches below the surface in the moor lying to the north- 
east of that hill. Decayed vegetable matter had something 
to do with the re-deposition. 
I must not omit heated waters and vapours. Their solvent 
