574 EOCENE AND OLIGOCENE PERIODS 



Marine Life 



The name Eocene (dawn of the recent) was meant to imply the 

 presence of less than 5% of living species among the marine inverte- 

 brates of the period; but most existing orders, families, and genera 

 were established. The changes of later times are considerable, and 

 are valuable as criteria for correlation, climatic changes, migrations, 

 etc., but they are not profound biological transformations. They 

 are in striking contrast with the radical and rapid evolution of the 

 mammals. 



Geologically, the most striking feature of the marine Eocene life 

 was the extraordinary abundance and size of the foraminifers 

 (Fig. 481). Most types of marine invertebrates had assumed their 

 modern forms. 



The American Eocene faunas were rather pronouncedly pro- 

 vincial, though some species have a rather wide range. So pro- 

 nounced is their provincial character that much difficulty is experi- 

 enced in making correlations between formations along different 

 parts of the Atlantic and Gulf coasts, and greater difficulties arise 

 in regions more widely separated. The variations are, however, 

 variations of detail, not of broad features. 



The marine fauna of the Pacific coast, 1 and the flora as far north 

 as Puget Sound, indicate a subtropical climate. 



OLIGOCENE FORMATIONS 



North America. Formations corresponding to the Oligocene 

 of Europe have not been differentiated completely in North Amer- 

 ica; 2 but certain formations along the Atlantic and Gulf coasts, 

 formerly classed as late Eocene or early Miocene, may be regarded 

 as equivalent to some part of the Oligocene of Europe. In the 

 Gulf region the Vicksburg (below) and Grand Gulf formations of 

 Alabama, Mississippi, and Louisiana, and the Fayette formation 

 of Texas, belong to this category. The early Oligocene is repre- 

 sented generously about the Caribbean sea, where its association 



lenticularis (Rogers); k and I, Venaricardiamarylandica Clark and Martin; m and 

 n, Corbula aldrichi Meyer; o and p, Protocardia levis Conrad; q, Ostrca compressi- 

 rostra Say; r, Modiolus alabamensis Aldrich; s, Lucina aquiana Clark; t, Leda 

 parilis (Conrad) ; u, Crassatellites alaformis (Conrad) ; v, Nucida ovula Lea; w, Pectcn 

 choctawensis Aldrich. (Maryland Geol. Surv.) 



1 Arnold, Jour. Geol., Vol. XVII, p. 509, and Knowlton, Tacoma, Wash., Folio. 



2 Ball, i8th Ann. Kept., U. S. Geol. Surv., Pt. II. 



