2 MR GOODCHILD ON 
then usually pass into the crystalline form.* The lime is 
left under these new conditions in chemical combination 
with some of the other constituents of the newly-formed 
rock, generally in combination with silica. The proportion 
of lime to the other constituents varies within wide limits, 
being small in rocks allied to granites, and ranging up to 
nearly 9 per cent. by weight in such rocks as those, for 
instance, which form Edinburgh Castle Rock, Salisbury Crags, 
the Corstorphine Hills, or the main mass of Arthur Seat. 
We may speak of these rocks as basalts. The percentage 
may be more than that in some rocks of exceptional character. 
When such rocks are exposed at the earth’s surface, they 
begin at once to be attacked by atmospheric agencies, and, in 
course of time, are almost entirely decomposed by them. A 
small quantity of Carbonic Acid (from +22 per cent. to ‘45 per 
cent. by volume) is carried down in solution by rain, and 
this quantity is considerably augmented when the rain-water 
reaches the surface, by acids of similar character (the humus 
acids), which arise through the action of bacteria upon dead 
plants and animals. Water charged with weak solutions of 
these acids possesses, amongst other properties, that of being 
able to decompose eruptive rocks. They effect this by 
forming bicarbonates of some of the constituents of these 
rocks, amongst which bicarbonates that of lime usually forms 
a large part. Any other lime-bearing rock suffers more or 
less from the attacks of the same chemical agency. Give it 
time enough, in fact, and Carbonic Acid is competent to dis- 
solve a large part of such lime-bearing rocks. Running water 
than carries the dissolved materials from the land surface 
downward, and in course of time transports the solutions to 
the sea. Other compounds of lime, of somewhat lesser 
importance in the present connection, are also liberated from 
rocks by chemical action, and are also transported seawards 
by means of rivers. Taking the basin of the Atlantic as an 
example, we find that lime-salts equivalent to nearly 54 
tons of carbonate of lime, are carried annually into the sea 
* The author has long taught in his Geology lectures that many of the 
phenomena connected with the so-called ‘‘ igneous” rocks are most satis- 
factorily explained by the hypothesis that these rocks are really deposits from 
aqueous solutions, 
