JURASSIC PERIOD. 465 



t 



culcttus, D. ovalis; Terebratula diphya, T. various, Ostrea Marshii (fig. 723), 

 0. gregaria, Gryjiliaea dilatata, Trigonia elongata, Astarte ovata; Ammonites 

 Jason, A. coronatus, A. Calloviensis, Belemnites hastatus. 



(2.) Coral Limestone (Coral Rag). — Ajnocrinus Royssianns, Hemicidaris cre- 

 nidaris, Cidaris coronata, Pygaster patelliformis ; Ostrea gregaria, Trigonia 

 Bronnii, T. costata, Diceras arietipa (fig. 728), Astarte elegans, A. minima (fig. 

 727); Pleurotomaria granulata, Nerinsea fasciata, N. Goodhallii ; Ammonites 

 Altenensis, A. plicatilis. At Solenhofen, Pterodactylus erassirostris (fig. 739), 

 and other species. 



6. Upper Oolite. — (1.) Kimmeridge Clay. — Ostrea deltoidea, ExogyraVirgida 

 (fig. 724), Trigonia muricata, T.clavellata (fig. 726), Cardium striatulum ; Nerinsea 

 Gosse ; Ammonites decipiens, A. rotundus, A. biplex. 



(2.) Portland Stone. — Ostrea expansa, Trigonia gibbosa, T. elongata, T. clavel- 

 lata (fig. 726), Lucina Portlandica, Cardium dissimile, Mactra rostrata ; Natica 

 elegans ; Ammonites biplex, A. giganteus. 



7. Purbeck Beds. — Hemicidaris Purbeckensis ; Ostrea distorta, Paludina 

 carinifera ; Cyjiris (various species); Mantellia megalophylla. 



III. General Observations. 



American Geography. — From the outcropping of the Jurassic 

 beds along the Black Hills and the flanks of the Eocky Mountains, 

 Hayden & Meek have inferred with good reason that these rocks 

 probably underlie the wide-spread Cretaceous strata of the eastern 

 slope of the Rocky Mountains ; and, as the elevation of the Rocky 

 chain above the ocean was not completed until long after the 

 close of the Cretaceous period (although it may have been begun 

 before it), we may infer that the condition mentioned as cha- 

 racteristic of the Triassic period — a shallow submergence beneath 

 an inland sea (p. 442) — was followed in the Jurassic period by 

 a somewhat deeper submergence, or at least that the waters 

 communicated directly with the ocean, so that marine life once 

 more covered the Rocky Mountain region from Kansas westward 

 beyond the summit of the chain, and in these shallow seas lime- 

 stones were forming again, as in the latter half of the Carboni- 

 ferous age. 



The absence of sea-shore Jurassic beds from the Atlantic border 

 leads to the same conclusions with regard to the coast in the Ju- 

 rassic period that were deduced for the Triassic (p. 442). 



European Geography. — The Jurassic period commenced in 

 England with the marine deposits of the Lias. Through the Oo- 

 lite the alternations were very numerous, indicating oscillations 

 between clear seas and shallow water or half-emerging land, in the 

 course of which there were coral reefs in England and Europe. 

 The evidences of shallow water and emerging flats increase to- 



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