TERTIARY PERIOD. 511 



cisco; in many parts of the San Joaquin and Tulare valleys, in the Estrella 

 valley, Santa Inez Mountains, San Raphael Hills ; at Ocoya Creek ; along the 

 flanks of the Peninsula range in the latitude of San Diego, etc. Both north 

 and south of San Francisco, on the coast, there are metamorphic slates, partly 

 talcose, which are either Tertiary or Cretaceous : and the talcose slaty rock 

 containing the Quicksilver mines, between San Francisco and Monterey (at 

 New Almaden and in that vicinity), is supposed to be part of the series. 



The strata at Gay Head, beginning below, are (1) Clay, filled with Turritella 

 alticostata, Callista (Cytherea) Say ana, etc.; (2) Sand, with few shells, chiefly 

 Yoldia (Nucula) limatula; (3) a sandy bed made up mostly of Crepidula costata ; 



(4) coarse ferruginous sand. Two miles off, the layer of Turritellse has changed 

 to a layer of Orepidulse, and the continuation of the Crepidula layer is filled 

 with Pectens, Venus difformis, Ostrea, etc. 



At a locality on James River, Va., there are (1) a layer of shells of Pecten 

 and Ostrea, 5 feet; (2) bed of Chamse, 3 feet; (3) bed of Pectens with Ostrese, 1 

 foot; (4) second bed of Chamse, with Area centenaria, Panopsea reflexa, 6 feet; 



(5) bed of large Pectens, 2 feet; (6) closely compacted bed of Chamse and Venus 

 difformis, 3 feet; (7) sand and clay separated from the preceding by a thin 

 layer of pebbles. But in other localities of the same region the beds are dif- 

 ferent. The first layer over the Eocene often consists of pebbles or coarse 

 sand. 



One of the most remarkable deposits in the Virginia Tertiary is a bed of In- 

 fusorial remains occurring near Richmond. It is in some places thirty feet 

 thick, and extends from Herring Bay on the Chesapeake, Md., to Petersburg, 

 Va., or beyond, and is an accumulation of the siliceous remains of microscopic 

 organisms, mostly Diatoms. Some of the beautiful forms are represented, much 

 magnified, in fig. 792 B. These beds have been referred both to the Miocene 

 and Eocene : they are called Eocene by Professor Rogers after an examination 

 of the region. 



A still thicker bed — exceeding fifty feet — exists on the Pacific at Monterey ; 

 the bed is white and porous like chalk, and abounds in siliceous organisms. 

 (Blake.) 



Sumter Epoch. — Pliocene. — The beds of the Sumter epoch occur in North and 

 South Carolina, extending south as far as the Edisto River. They contain forty 

 to sixty per cent, of living species of shells. (Tuomey & Holmes.) The beds are 

 soft, either loam, clay, or sand, and lie in depressions of the older Tertiary and 

 the Cretaceous formations. Unless these beds are the equivalents of the Vir- 

 ginia Miocene, they are not represented, as far as now known, in Virginia or 

 farther north. No beds of this epoch have been reported from the Gulf States. 



In the Upper Missouri region the White River group is overlaid by other fresh- 

 water Tertiary beds, 300 to 400 feet thick, called by Meek & Hayden the Loup 

 River group. They contain in their upper part the remains of numerous ex- 

 tinct Mammals, including Camels, Rhinoceroses, Elephants, etc., besides land 

 and fresh-water shells which are probably of recent species. These beds occur 

 on the Loup Fork of the Platte, and stretch north to the Niobrara and south 

 beyond the Platte. The fossils are supposed to be of Pliocene age. 



