Mississippian synonyms

This older classification, which has little support except that which is traditional, is still adhered to by many geologists; hut the fact seems to be that the system is set off from the Pennsylvanian (Upper Carboniferous) more sharply than the Cambrian is from the Ordoviciao, the Silurian from the Devonian, or the Devonian from the Mississippian.

Superficially, each is a simple rolling plateau, much broken by erosion (though considerable undissected areas drained by underground channels remain), especially in the east, and dotted with hills; some of these are residual outliers of the eroded Mississippian limestones to the west, and others are the summits of an archaean topography above which sedimentary formations that now constitute the valley-floor about them were deposited and then eroded.

(See Bernician, Tuedian and Avonian.) At an early period, owing to the immense commercial importance of the coal seams, it became the practice to distinguish a " productive " (flotzfiihrend, terrain houiller) and an "unproductive," barren (flotzleerer) Lower Carboniferous; these two groups correspond in North America to the " Carboniferous " and " Sub-Carboniferous " respectively, or, as they are now sometimes styled, the " Pennsylvanian " and " Mississippian."