Orotdxis : A Metliod of Correlation. — h'ei/es 
2'.)'.» 
abrupt modification in sedimentation, and consequent!}' in 
lithological, stratigraphic, faunal, and in fact all characters, 
are those connected directly with diastatic change, producing 
depression of some land areas below sea level, and the upris- 
ing of other districts above the level at which they once 
stood, to form those great features of the earth's surface 
called mountains. Geological chronology, therefore, is be- 
lieved to find a true and rational basis in those changes 
which primaril}^ govern sedimentation and which are inti- 
mately connected with the genesis of mountain systems. It 
is proposed, therefore, to emphasize this factor as funda- 
mental in the marking of the leading subdivisions of geolog- 
ical time and to define general stratigraphical succession in 
accordance with the cycles of orographic development, calling 
the classification or fundamental principle of correlation a 
systematic arrangement of mountains, or orotaxis. 
B}^ the term mountains, is meant not alone those geograph- 
ic features which, at the present time, rise so majestically and 
conspicuously from the surface of the earth, but also all of 
those structures which have been in the past prominent char- 
acters in the surface relief, and which, geotectonically, are 
still mountains, though i)erhaps now completely base-leveled 
or long since buried beneath later sediments. With these old 
mountains the ("ycles of orographic development are pro])erly 
regarded as extending from the time when the strata were 
compressed, through the periods when the}?^ were bowed uj), 
then planed off nearly to sea-level, and submerged, perhaps, 
until new degradational products were deposited upon their 
upturned edges. The completed cycle of mountain-nuiking is 
the measure of orotaxial chl•onolog3^ The division ])lan('s 
cutting the geological column into systems, series, or smaller 
parts, are actually, as well as theoretically, the lines of uncon- 
forinities and their representatives. In the case of the more 
extensive ones they do. no doubt, represent base-leveletl sur- 
faces or peneplains. 
In all eases, great or small, tin.' erosion i)laiic and the ix-rifid 
of degradation of the land has its eijuivalent in the sea in an 
accumulation of sediments. An ancient ])lane of unc(uiforiii- 
ity, as it is now open to observation, may pass gradually int(v 
a great })lain of sedimentation. In the graiidei' uuconrornii 
