Clarke — The Naples Fauna. 



39 



of the fauna was effected, stragglers here and there having continued for a 

 while under the changed conditions, until the Intumescens-fauna comes back 

 again into this region intensified in vitality and specific representation during 

 the period represented by the Naples beds. 



Such recurrences of faunas are to be always expected in the displacement 

 of one fauna by its successor, and many excellent illustrations of such 

 phenomena are afforded in the palaeozoic sections of this state. The writer 

 has called attention to a recurrence of the fauna of the Marcellus shales after 

 the introduction of the normal fauna of the Hamilton shales (Fourth Ann. Rept. 

 N. Y. State Geol. p. 15, 1885) ; a recurrence of characteristic species of the Corni- 

 ferous limestone above the base of the Marcellus shales ( Thirteenth Ann. Rept. 

 N. Y. State Geol. pp. 119-156, 1891), and a preliminary appearance of the normal 

 Hamilton fauna in the midst of the Marcellus shales, in a persistent stratum 

 which has been termed the "Stafford limestone " (Eighth Ann. Rept. N. Y. State 

 Geol. p. 60, 1889 ; Thirteenth Aim. Rept. N. Y. State Geol. pp. 118, 157, 1891). 

 In all of these instances the reappearing fauna accompanies a reiteration of its 

 normal conditions of sedimentation. It will be observed that these occur- 

 rences are not all recurrences. Certain of them are introductory and incom- 

 plete representations of the fauna at its normal development ; thus there are 

 precurrent or prenuncial faunas, such as that of the Stafford limestone with 

 reference to the Hamilton fauna, and that of the Styliola limestone with 

 reference to the Naples fauna. Some are post-current faunas, imperfect repre- 

 sentations of faunas whose normal or culminating development has passed, like 

 the reiterations of the Marcellus fauna in the Hamilton shales, as just cited. 



The Styliola limestone, thus, contains the prenuncial Intumescens-fauna. 

 Its appearance was abrupt, and we shall have occasion to observe after close 

 analysis, that in the great majority of its components it was an exotic fauna. 

 This is emphatically shown in the inrush of goniatites and lamellibranehs 

 novel to American faunas, all of forms which especially characterize this assem- 

 blage. With them are intermingled some species which may have persisted 

 from previous faunas in the same region but they are few and less characteristic. 



The Normal Fauna. The Naples fauna, or the normal Intumescens- 

 fauna, is always best developed in the soft, compact, sandy shales of 

 the lower part of the rock series. The bituminous deposits of the epoch 

 of the Genesee are terminated by a gradual increase of arenaceous matter in 

 the sediments, which eventually introduces greenish flags and rather thick 

 sandstones as the basal strata of the Portage group. 



In Seneca county, the Genesee slate is, as shown by the recent investiga- 

 tions of D. F. Lincoln, capped by a very impure bituminous nodular limestone. 



