220 Observations upon the Geology and Paleontology 



The preceding table shows that a few of the species are 

 common to all the beds from No. 1 to the middle portion 

 of No. 7, inclusive, and that other species commence below 

 the upper limit of these, and range through both beds of 

 Burlington limestone. In separating the fossils thus asso- 

 ciated, we feel bound to consider those as Devonian species 

 w^hich have their origin and greatest development in rocks 

 of known Devonian age, and are found above the proper 

 limit of these rocks only in their decline. But we must, 

 nevertheless, regard those species as Carboniferous which 

 have their greatest development in Carboniferous strata, 

 although they may have originated among Devonian 

 forms. 



This table will show, at a glance, how closely these 

 Devonian and Carboniferous rocks are linked together by 

 the association of their fossils ; but it is not expected that 

 it will give a full expression of the fossils of the whole 

 series, or even of the shells alone. The shells here given 

 are only those which are best known, while many other 

 recognized species, not yet described, are omitted, among 

 which are some that would perhaps illustrate still more 

 fully the Chemung character of the lower beds than those 

 enumerated. 



The following table comprises a list of all the genera 

 that have been recognized here ; and, being arranged like 

 the preceding one, will also show in which beds each 

 genus has been recognized. This arrangement will show 

 the generic relations of the upper and lower beds, but not 

 their specific relations. Some of the genera are marked 

 with an interrogation point, expressing doubt as to their 

 identity, in consequence of the specimens being in a bad 

 state of preservation. It is probable that other genera 

 than those enumerated may yet be discovered. 



