250 
POPULAR SCIENCE REVIEW. 
In commencing the study of chemical geology, the student 
should, above all things, avail himself of every opportunity for 
experimental research, always bearing in mind, however, that 
geology, not chemistry, is his starting-point ; and that, conse- 
quently, his laboratory must be made, as it were, subservient to 
his work in the field, yet at the same time go hand in hand 
with it. 
There appears to be an innate tendency in man to take up a 
favourite cause or hypothesis, to which are often attributed effects 
in reality the result of some very different agency, or which may 
be due to the combined action of several causes ; and for this 
reason the student should be particularly careful not to attach 
himself to any special theory or school of geology which might 
bias him when estimating the value of evidence brought for- 
ward on both sides o/ any question under consideration. 
The partisans of the so-called Plutonic and Neptunic, or 
igneous and aqueous schools of geology, have apparently quite 
forgotten how difficult, if not impossible, it is, in the study of 
Nature’s operations, to draw any sharp line of demarcation as 
to where any one cause ceases and another commences to operate, 
and have each in turn attempted to make the action of fire or 
water alone, account for effects which no impartial investigator 
can for a moment doubt, have been, at least in many cases, the 
result of a combination of both agencies. 
Since the action of fire, water, and gases must be regarded 
as the most important agencies by which chemico-geological 
changes have been brought about in our globe, it becomes of the 
utmost importance that the terms igneous, aqueous, and gaso- 
lytic action, when applied in the study of geological phenomena, 
should be defined with some precision. 
Igneous action is, in other words, volcanic action — that is, the 
action of heat as seen developed in active volcanoes, the study 
of which led to the formation of the Plutonic school of geolo- 
gists. This is not a mere- dry fusion, like melting lead, glass, 
or other anhydrous substances in a crucible, but is one in which, 
whilst heat plays the grand role, is in nature invariably accom- 
panied by the action of the vapour of water and gases. 
Aqueous action is the action of waters (fresh or saline) such 
as are seen on the present surface of the globe ; and is not the 
mere solvent action of pure water, but is one in which the air, 
gases, salts, and other bodies contained in natural waters, as- 
sisted by heat, materially alters the solvent powers and chemical 
reactions of the water itself. 
Grasolytic action is the effect of gases and vapours, more or 
less assisted by heat. 
All these agencies are naturally modified by the effects of 
chemical action and mechanical force. In all three cases, the 
