834 



HISTORICAL GEOLOGY. 



Queen Charlotte Islands he has announced Dioonites Columhianus Dawson. From the 

 Kootanie beds of Montana at Great Falls, Newberry has described (1891) 25 species of 

 plants, and among them, Zamites Montana, Z. acutipennif<, Z. borealis Heer, Z. apertus 

 Newberry, Podozamites nervosas Newb., Sequoia Smittiana Ileer, S. gracilis Heer, S. 

 Beichenbachi Heer, and Sphenolepidium Virginicum Fontaine. The last two are also 

 found in the Potomac group. From the Trinity groui) of Texas, Fontaine has identified 

 some Neocomian species: as Dioonites Buchianua, D. Dunkerianits, Abietites Linkii, 

 and a species very near Sphenopteris Valdensis, besides several other species that occur 

 in the Potomac group. 



1357. 



RmzopoD. — Patellina 

 Texana. Eoemer. 



1358. 



Animals. — Marine fossils are confined almost solely to the beds of Texas 

 and Mexico, and tlie Pacific Coast region ; and these two regions widely diif er in 

 fauna. The former was apparently tropical, while the 

 latter bears evidence of cooler waters, just as the Mexican 

 Gulf and California seas now differ. At present this dif- 

 ference (as shown on the isocrymal chart, page 47) is 

 about 16° F., owing to the cold currents that descend the 

 Pacific coast from the north; and it was probably 10° or 

 12° in Cretaceous times, when like species occuri-ed on that 

 coast from California to Alaska. 



Texas. — The Comanche beds are largely made of the 

 minute shells of Rhizopods, and also contain the larger 

 ISTummulite-like fossil, the Patellina (OrhitulUes) Texana (Fig. 1357). Echi- 

 noderms are represented by 

 species of Enallaster (Fig. 

 135^) , Pseudodiadema, Hemi- 

 aster, Cidaris, etc. ; Brachio- 

 pods, by species of Terebra- 

 tula. 



Lamellibranchs occur of 

 the genera Oryphma (Fig. 

 1359), Exogyra (Fig. 1360), 

 Lima, Inoceramus, which are 

 very common. Some speci- 

 mens of Exogyra ponderosa 

 in Texas are nine inches long, 



and the shell four inches thick at middle. Two species of genera related 

 to the modern Chama, peculiar to the Cretaceous, are RadioUtes Texanus (Fig. 

 1361, 1361 a), reduced from a length of 41 inches, and Requienia (Caprina) 

 Texana (Fig. 1362). The genus Nerinea (Fig. 1363) is also characteristic 

 of the Cretaceous. 



Of the fossils of the Shasta group, California, the Aucelloi are especially 

 characteristic. The forms vary much, but all are referred to one species 

 named by Gabb, A. Piochii. Fig. 1364 represents a common form of the 

 shell, and Fig. 1365, the smaller valve of a specimen. Another specimen 

 figured has a height of more than two inches, while but little wider than 



ECIIINODEKM. - 



■Enallaster Texaims, upper and under surface. 

 Ecemer. 



