430 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



The nicety and rapidity with which the orotaxial principles act 

 in practice are indicated by a number of specific determinations. 

 Furthermore, in the Upper Mississippi Valley the relative values 

 of the different methods of correlation are capable of exact com- 

 parison. 



In the present advanced stage of stratigraphical science, when 

 reconnaissance work is no longer needful over a large part of our 

 country, it appears that we have reached a point at which classifi- 

 cation of geologic terranes begins to follow definite rules in ac- 

 cordance with the taxonomic ranks of the several geologic units, 

 much in the same way that it is accomplished in botany or zool- 

 ogy. We may arbitrarily recognize the larger subdivisions as world- 

 wide time units; and regard the sediments as deposited during 

 certain cycles, or periods. The latter may also be again subdivided 

 and still retain the time criterion. Below the taxonomic rank period, 

 or sub-period, geologic sections become provincial in character. By 

 clearly distinguishing between geologic history and biotic history 

 geologic correlation is placed upon a rational, genetic, and philo- 

 sophic foundation. Thereby is stratigraphy immeasurably advanced. 



MOUNTAIN STRUCTURES UNDER THE PRAIRIES 



That mountains should once spring forth where now is level 

 land is one of the scientific novelties of our State. Of all places 

 on earth the flat and monotonous plains are the last place where 

 one would be inclined to look for traces of Alpine scenery. Yet 

 mountains here there once surely were, albeit they now are com- 

 pletely vanquished, leveled to the sea, lost and forgotten. That 

 there lie buried under the surface of the smooth illimitable prairie 

 land the remains of a high and mighty range is a circumstance 

 almost inconceivable. Although at the present day the suggestions 

 of these old mountains are inconspicuous they are many. Through 

 means of records of deep-well borings and other data, the height, 

 extent, and form of the ancient mountains are fully figured forth 

 and their characterjstic features pictured out. 



This great earth-wrinkle, which sprang from the sea in Alesozoic 

 times, extended from the east shore of present Lake Superior south- 

 westward beyond the path of the Missouri river. Medially the 

 strata were bowed up more than a mile above the existing level 

 of the prairies. In their prime these Siouan Mountains rivaled in 

 scenic beauty and stately grandeur the Adirondacks, the southern 

 Apj)alachians, or the Juras of today. 



