59 8 THE MIOCENE PERIOD 



or destroying the previous warm-water fauna of the region, and 

 bringing with it a cold-water fauna. There was a complete change 

 of species, and even some genera were displaced. The fauna re- 

 tained, however, a general molluscan aspect. Both the bivalves 

 and the univalves gave proof of better adaptability to the vicissi- 

 tudes of the coastal tracts than most other forms, and held their 

 dominance. Figs. 498 and 499 show a few characteristic types. 

 Compared with the Eocene group, Fig. 482, the resemblances will 

 be found more striking than the differences. 



The marine fauna of the Pacific coast indicates a climate but 

 little warmer than that of the present, and this conclusion is re- 

 enforced by the plants of the Puget Sound region, which record 

 a transition from the subtropical climate of the Eocene to the tem- 

 perate climate of the present. The fauna of the Upper Miocene 

 indicates a still closer approach to the present. 



alticosta (Conrad); o, F. griscomi (Conrad); p, Xenophora conchyliophora (Born); 

 q, Crepidula fornicata (Linn6) ; r, Fulgar spiniger (Conrad) var. ; s, Ecphora quadri- 

 costata (Say); t, Siphonalia marylandica Martin; , Ilyanassa (?) (Paranassa) 

 porcina (Say). Scaphopod: v, Dentalium attenuatum Say. (Maryland Geol. Surv.) 



