G 
METHODS OF THEORIZING IN GEOLOGY. 
[Ch. I. 
the ordinary economy of Nature. If, for example, we seek for 
the causes why mineral masses are associated together in certain 
groups ; why they are arranged in a certain order which is never 
inverted ; why there are many breaks in the continuity of the 
series; why different organic remains are found in distinct sets 
of strata ; why there is often an abrupt passage from an assem- 
blage of species contained in one formation to that in another 
immediately superimposed, — when these and other topics of an 
equally extensive kind are discussed, we find the habit of 
indulging conjectures, respecting irregular and extraordinary 
causes, to be still in full force. 
We hear of sudden and violent revolutions of the globe, of 
the instantaneous elevation of mountain chains, of paroxysms 
of volcanic energy, declining according to some, and according 
to others increasing in violence, from the earliest to the latest 
ages. We are also told of general catastrophes and a succes- 
sion of deluges, of the alternation of periods of repose and 
disorder, of the refrigeration of the globe, of the sudden anni- 
hilation of whole races of animals and plants, and other hypo- 
theses, in which we see the ancient spirit of speculation revived, 
and a desire manifested to cut, rather than patiently to untie, 
the Gordian knot. 
In our attempt to unravel these difficult questions, we shall 
adopt a different course, restricting ourselves to the known or 
possible operations of existing causes ; feeling assured that we 
have not yet exhausted the resources which the study of the 
present course of nature may provide, and therefore that we are 
not authorized, in the infancy of our science, to recur to extra- 
ordinary agents. We shall adhere to this plan, not only on 
the grounds explained in the first volume, but because, as we 
have above stated, history informs us that this method has 
always put geologists on the road that leads to truth, — suggest- 
ing views which, although imperfect at first, have been found 
capable of improvement, until at last adopted by universal 
consent. On the other hand, the opposite method, that of 
speculating on a former distinct state of things, has led inva- 
riably to a multitude of contradictory systems, which have been 
