Orofaxis : A Jfef/iotJ of' ( orrc/af /<>/>. — h'ci/es. -295 
While it was widely recognized that the biotic criteria are 
not entirely adequate for purposes of general correlation, it 
remained for those working in terranes which were wholh' de- 
void of organic remains to devise special methods for reaching 
the same end, methods which were entirely physical in charac- 
ter. The great object attained by the elaboration of these 
methods has been to point out that in the systematic arrange- 
ment of formations, satisfactory results are not only possible 
but that the relationships established are equally accurate 
and the methods equally as applicable practically as the most 
refined biotic methods 3'^et used. 
Since the classification of the Arcluean (including Al- 
gonkian) was given up as impossible without the aid of fos- 
sils, Irving and Van Hise have formulated admirable methods 
of working, in which organic remains are left entirel}' out of 
consideration. McGee and his colleagues have, by purely 
physical methods, attacked the unfossiliferous deposits of the 
Coastal plain, and then have applied the same methods suc- 
cessfully to the fossiliferous terranes. Davis and others have 
rejuvinated the old methods of stratigraphical continuity 
and lithological similarity, by making possible a system of 
correlation by geographic forms, and broad areas are now 
being geologically mapped by this method alone. All of these 
methods are more or less complex and not simple, but the}' 
demonstrate that newer and more natural ways are rapidly re- 
placing the older and more artificial ones, and that there is 
ample hope for devising physical means of correlation that are 
more in harmony with the real nature of the problems involved. 
With the waning influence of the chief criterion which has 
long held sway in the accepted system of correlation the ne- 
cessity gradual!}' becomes manifest for a plan which is more 
in accord with the recent rapid progress and unparalled ex- 
pansion of geological knowledge. Of the suggestions that 
have been offered of late years, for the establishmeiit of a 
scheme of geological correlation independent of fossil evidence, 
the three just mentioned are especially prominent and are cer- 
tainly destined to have wide utility and to be fruitful of grand 
results. By a combination, modification, and expansion of 
the centralideas of all these, together with the legitimate use 
of the cardinal principles involved, it is believed that a scheme 
