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IOWA ACADEMY OF SCIENCE Vol. XXVIII, 1921 
trasts, but they carry westward the regional diastrophic record so 
clearly decipherable in the east, and indicate a succession of geo- 
graphic cycles which the Great Basin has no doubt passed through 
but of which it has now no other intimations. 
In the High Plateaux region there appear to be presented in the 
post-Paleozoic section five distinct, wide-spread, and notable hori- 
zons of unconformity which represent erosion intervals of vast 
duration and intensity. Their stratigraphic positions coincide 
exactly with similar erosion plains in the rock-column on the east 
flank of the Rocky Mountain uplift. These levels are also trace- 
able around the southern extremity of the Cordillera, so that their 
identifications are seemingly fixed beyond peradventure. 
Age 
East Side, r.m. 
R.M. Crest 
West Side, r.m. 
Present 
General plains surface 
Stream valleys 
Plains surface 
Miocene 
Maya 
Obliterated 
Markagunt 
Laramie 
Raton 
Obliterated 
Aquarius 
Comanchian 
Corazon 
Summital 
Paunsagunt 
Jurassic 
Tucumcari 
Central monadnocks 
Rafael 
