ie eGE NE Die sel ASSIFICATION OF GEOLOGIC AE 
PHENOMENA. 
In the consideration of every branch of natural knowledge, one 
of the first phases to receive attention is some ready means of com- 
paring the various phenomena presented. Gradually there grows 
up some systemization of the facts and principles, that after- 
wards reflects the particular stage that the branch at that time 
attained. This orderly arrangement is the initial step in raising 
the branch to the dignity of a science. 
Scientific advancement may be measured by the degree of 
taxonomic completeness shown, and by the character of the 
criteria regarded as critical. As progress is made a rapid evolu- 
tion in the fundamental plan of grouping the facts takes place. 
In the beginning, a classification, crude though it may be, is out- 
lined from those superficial features that, at first glance, are the 
most striking. This is, at a later stage, modified to one in which 
similarity of common characters, irrespective of natural relations, 
is taken into account. A vastly more advanced conception is 
classification based upon affinity, in which for similarity of fea- 
tures is substituted similarity of plan. The final stage is one in 
which origin, or causal relationship, is the governing principle. 
This is genetic classification. 
At the present time the science of geology is just entering 
upon the stage last mentioned. As yet, no complete genetic 
scheme has been proposed. However, various attempts have 
been made to emphasize the principle of genetic association. 
All of these efforts appear to be too closely wrapped up in the 
older conceptions to show very much real advancement over 
them. They plainly indicate that the time is now ripe to seri- 
ously plan for a purely genetic arrangement of geological phe- 
nomena. 
The older text-books on geology treat of all things geological 
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