OF DENISON UNIVERSITY. 
99 
in fauna than those of different lithological character lying closer to- 
gether or even between them. (That is, vital conditions may much more 
rapidly change along the shore than in deposits of the same age out at 
sea.) 
Thus in the study of the phylogeny of the fauna of a shale, it 
should be compared with that of the next following shale and not of 
the intervening sandstone, but it must be remembered that the period 
intervening is probably represented by the deposits of the same bed in 
the direction of the encroachments of an ascending sea or the flight of 
a retreating one. 
6. Opposite sides of the same basin may vary greatly in fauna. 
4. Adjacent basins of the same age are rarely identical in fauna 
and it may be that the most abundantly represented species of these 
basins are unlike while the rarer species are identical, the latter there- 
fore being most reliable age-indices. 
8. It is to be expected that opposite sides of the same basin will 
possess vicarious species or varieties, and that corresponding sides of 
separate basins may be more nearly alike than adjacent sides. 
9. Adjacent basins may have their strata intermingled along the 
margin through the agency of unequal oscillation of the sea bottom in 
the several basins. Then there will result the spurious appearance of 
an alteration of faunas in one terrane when in reality, instead of the 
consecutive strata representing changes in one basin, they represent 
conditions in distinct sea basins, 
10. Under favorable conditions, a local fauna may persist long 
after the normally associated groups have elsewhere perished. 
The above are but a few of the many considerations which the 
student should bear constantly in mind in attempting the correlation 
of distant or even adjoining strata. 
As a basis for further study let us briefly examine the Waverly 
series as it appears in central Ohio. The headings will sufflciently 
forecast the conclusions reached and the reader is asked to postpone 
judgment as to their correctness until after perusing what follows and 
examining the tables of distribution of species. 
III. Keokuk and Burlington Groups. 
Upper Waverly. (Upper Logan.) Embracing shales and free- 
stone (the latter disappearing north-eastward) susceptible of sub- 
division into several tolerably distinct zones. 
