MESOZOIC TIME — TRIASSIC AND JURASSIC. 793 



heat, flowing northward and eastward near its eastern border, but not much 

 for the warming of Korth American waters north of Cape Hatteras ; its 

 heat is carried on for distribution over northern and western Europe and the 

 Arctic seas. Heading off the Gulf Stream from the American coast north of 

 Hatteras, there flows from the north a current of Arctic waters, that makes its 

 escape from the polar basin by the only large passage way out — the way 

 leading into the Atlantic ; and these cold waters are like a cold wall along 

 the eastern side of the continent. The American coast has a means of pro- 

 tection against the polar current, through an elevation of the border sufficient 

 to make Newfoundland a peninsula by closing the Strait of Belle Isle. 

 Moreover, if the elevation were only 500 feet, the eastern cape, around which 

 the cold current would be forced to flow, would be set 250 miles east of its 

 present position. 



On the Pacific side a cold northwestern current follows the coast of North 

 America from Alaska southward, as part of the normal oceanic circulation. 



Thus at the present time North America has relatively cold waters along 

 both its eastern and western shores. Hence there is reason enough for the 

 paucity of its existing marine faunas. In Paleozoic time this contrast with 

 Europe did not exist, or only to a small degree ; for the Paleozoic species even 

 exceed in numbers those of Europe. The Arctic basin was probably op3n 

 widely in all directions. But in the early Mesozoic it must have become the 

 closed basin which it now is, with its only free outlet into the Atlantic ; and 

 in this way the continent of North America was thus early put between 

 northern cold Atlantic and cold Pacific currents. 



The actual difference of temperature between the waters of the North 

 American and European sides of the Atlantic in the Triassic and Jurassic 

 periods is uncertain, because no marine fossils of these periods have been 

 found on the American side. On the European side the presence of warm 

 seas is proved by the profusion of marine species and by their kinds. The 

 coral reefs of the Oolyte in England consist of corals of the same group with 

 the reef-making species of the existing tropics. This favors the conclusion 

 that the British waters, and nearly all the European, were within the coral- 

 reef temperature limit ; that is, the line along which 68° E. is the mean tem- 

 perature of the year. The Oolytic isocryme of 68° E. (see map, page 47), 

 accordingly, would have had nearly the position of the line of 44° E. in exist- 

 ing seas, but with a little less northing and more leaning to the eastward. 

 The Gulf Stream was the probable cause of this long northward extension 

 of warm waters in Jurassic time. 



Further, in Europe, according to Neumayr, differences in the climate of 

 the later Jurassic are indicated by the distribution of fossil Invertebrates. 

 The Mediterranean Province, or that of southern Europe, including the 

 regions of the Alps and Carpathians, Italy, Spain, and the Balkan peninsula, 

 is characterized by Ammonites of the genera Phylloceras, Lytoceras, and 

 Simoceras, with the Brachiopod Terebratula diphya. The Middle European 

 Province, comprising the region of the Juras, France, Germany, England, 



