More than half a century has passed since the rich and varied faunas of the later Paleozoic rocks of the continental interior first began to attract attention. From the beginning an exceedingly active and ever-growing interest was taken in the various forms of ancient life represented, and, as a matter of consequence, the geological history of the region was approached from the biological rather than the stratigraphical side.
Especially was this the case along the line of the Mississippi river, where the most important exposures of the strata in question occur.
The relations of the most important horizons of the lower Carboniferous in the upper Mississippi valley were early made out by Owen and others, and although Owen’s views underwent considerable change during the dozen years that he was engaged in studying these rocks, his subdivisions have been practically the basis of all subsequent classifications. In the main . . .