GEOLOGICAL CLASSIFICATION. ‘i 115 
parallelism can be established between them and the subdivisions of the group of strata to which 
they are generally equivalent on other parts of this continent. 
If their mineral composition is a wholly unreliable guide in going from this side to the other 
of the Rio Grande, how much more questionable are inferences drawn from it on opposite sides 
of the Atlantic! 
In the foregoing section of Messrs. Meek and Hayden it will be observed that the Carboniferous 
fossils of the lower members extend up, mingling with Permian forms, to the base of No. 10. 
Here the last traces of that formation disappear; and No. 10 contains only fossils which are 
regarded in Europe as characteristic of the Permian rocks. Above No. 10 no fossils have been 
found below the sandstone (No. 1) which forms the base of the Cretaceous series. 
The intermingling of Permian and Carboniferous in the strata of this section is an interesting 
fact which has been remarked upon by Messrs. M. & H. It shows plainly that no line of 
demarcation can be drawn between these formations in the west; that the periods of deposition 
of all these rocks were but parts of one great epoch during which the same general physical 
conditions prevailed. There were, doubtless, marked local peculiarities in the physical geography 
of different districts on the continent—peculiarities recorded in the discrepancies I have referred 
to between the synchronous deposits of the banks of the Kansas and Little Colorado—but the 
strata are entirely confurmable both with the older rocks below and the Cretaceous beds above. | 
Throughout this interval the general lithological uniformity, in the many repetitions of the 
strata, evince greater stability, a longer period of geological rest, than has been indicated by 
the rocks of any other portion of the globe which has yet been examined. 
Such being the case, we shall probably look in vain for data which will permit us here to 
draw the lines which separate formations in other countries—or rather in books—sharply through 
the geological column. 
Geological classification is everywhere to some extent a conventionality, being without precise 
counterpart in nature; but on the great plateau west of the Mississippi lines of division between 
the different formations elsewhere (see p. 69) are not to be discovered; and the effort 
to apply rigidly to the rocks of that region the classification adopted in other countries will be 
but partially successful; this difficulty is felt by Meek and Hayden in attempting to define the 
limit between the Carboniferous and Permian rocks of Kansas. 
In Europe the line of demarcation is not very apparent; in Kansas it does not exist. If 
compelled to draw that line, however, it should doubtless be done, as they suggest, at the base 
of No. 10, where the last vestige of the fauna of the lower and more important formations 
disappear. 
