540 JOSEPH EE CONTE 
becomes irregular, and more and more so, until it is no longer 
discernible and all seems confusion. At certain intervals the 
leaders run along the lines hastening up the laggards until the 
line is re-formed. But the re-formed line again soon becomes 
irregular and falls into confusion, and is again re-formed, and 
so on. 
Of course partial and more or less local readjustments of 
synchrony and homotaxy take place at intermediate times at the 
end of subordinate cycles. Sometimes in the general readjust- 
ment some locality may be left out. This is the case with Aus- 
tralia today. The last wide migrations and minglings of faunas 
and obliteration of geographical diversity, viz., that during the 
Quaternary, did not reach Australia, and therefore its fauna is 
still far behind in the race of evolution. . 
4. Cycle of topographic forms by eroston.— But there is still 
another cycle, and one with which we are especially concerned 
here, viz., the cycle of erosion-forms. Every critical period is a 
time of the formation of great mountain ranges, and the crisis is 
usually named after the mountain range which forms its most 
conspicuous monument. Thus we have the Appalachian revolu- 
tion, closing the Paleozoic ; the Cordilleran, closing the Mesozoic. 
The pre-Cambrian crisis might well be called the Laurentian, 
and the one we are now specially dealing with, viz., the Quater- 
nary or Ozarkian, might well be called the Basin Ranges revolu- 
tion; for not only the basin ranges, but also the Sierra Nevada, 
the Coast Ranges of California, and the Mt. St. Elias Range of 
Alaska were either formed or else rejuvenated at that time. 
Thus with every critical period there are new mountains 
formed and old ones rejuvenated; new lands formed by emer- 
gence of sea bottoms and old ones elevated or depressed. Thus 
new constructional forms are made and a new cycle of destruc- 
tional or erosive forms inaugurated. These forms pass gradu- 
ally through the stages so graphically described by Professor 
W. M. Davis and others, the final result being the so-called 
peneplain. Of course, there are subordinate, intermediate, and 
more local cycles; and therefore at the end of the great cycle 
