582 C. SCHUCHERT PALEOGEOGRAPHY OF NORTH AMERICA 



landian." It is probable that there was also slight and temporary com- 

 inunication with the Pacific ocean. 



Similar but very late Upper Jurassic faunas occur at Malone, Texas, 

 and are described by Cragin. 233 



Continental deposits of the Great plains. — The Morrison formation, 

 having a thickness of from 200 to 400 feet, has been placed on the late 

 Upper Jurassic map (also on Early Comanchic map), yet the faunal evi- 

 dence is equally as good, and even better, for regarding this, the Bronto- 

 saurus horizon, as Lower Comanchic. There are here no direct marine 

 checks to fix the exact age of these deposits. They are, however, younger 

 than Middle Jurassic and older than Washita, or the upper third of the 

 Comanchic. According to Osborn, the mammals compare readily with 

 those from the English Purbeck at the very top of the Jurassic, while the 

 dinosaurs have long been regarded as Wealden in age, which Geikie and 

 most European geologists refer to the Neocomian, equivalent to the lower 

 part of the Comanchic. 



From this formation there have been described several species of Vnio, 

 Vivipara, Planorbis, Lioplacodes, Limncea, Vorticifex, and Valvata. Ac- 

 cording to C. A. White, 234 these fresh-water shells " of themselves offer no 

 suggestion of greater age than the Tertiary." The more characteristic 

 dinosaurs are: Atlantosaurus , Apatosaurus, Brontosaurus, Diplodocus, 

 Morosaurus, Stegosaurus, Camptosaurus, and Ceratosaurus. Of the small 

 Prototheria mammals may be mentioned: Allodon, Ctenacodon, Styla- 

 codon, and Diplocynodon. Small cycad trunks also occur in the Upper 

 Morrison (see further remarks on page 586). 



Maryland. — In eastern North America the lower basal part of the Po- 

 tomac series — that is, the Patuxent-Arundel — is often referred to the 

 Upper Jurassic. Berry has restudied the floral evidence and regards 

 these continental deposits as of Comanchic time. On the other hand, 

 Lull, from the evidence of the dinosaurs, finds the facts in harmony with 

 the age of the Morrison and Wealden. While as yet the proper systemic 

 reference of the Morrison and the Patuxent-Arundel is still unsettled, the 

 tendency is to refer both to the Lower Comanchic (also see page 586). 



Arctic Alaska. — A very thick series of continental deposits of Upper 

 Jurassic age was discovered by Collier 235 in the Cape Lisburne region of 

 Alaska. The series has a thickness of about 15,000 feet, in which there 

 -are 39 low grade non-coking coal beds, varying in depth from a few inches 



™ Cragin : Bull. no. 266, U. S. Geological Survey, 1905. 



23 * White : Bull. no. 29, U. S. Geological Survey, 1886 ; see also Stanton, Journal of 

 Geology, vol. 18, 1905, pp. 657-669. 



23 s Collier : Bull. no. 278, U. S. Geological Survey, 1906. 



