398 THE POPULAR SCIENCE MONTHLY 



ships of widely separated faunas. A large proportion of the Karnic 

 species of India is identical with the Mediterranean fauna^ and in Cali- 

 fornia about one third are common forms in the Alps and Sicily. 



Immediatelly above the beds with Tropites suhbullatus in India, the 

 Alps, and in California occur massive limestones full of coral reefs, with 

 some few identical species in all three regions. This same group of 

 ancient reef -builders has also been found in Alaska, in the same strati- 

 graphic position. This shows that the wide distribution of the Upper 

 Triassic species was made possible by the nearly uniform distribution of 

 warm water over a great part of the globe. 



In the latter part of the Upper Triassic widespread physiographic 

 disturbances had again divided the great zoologic regions. The Atlantic- 

 Pacific connection had disappeared, but there was still free communica- 

 tion between the Alpine province and the Orient, for Mediterranean 

 species reached as far as India and Timor. Around the North Pacific, 

 with the Arctic sea as its center of dispersion, a different fauna, that of 

 the bivalve, Pseudomonotis ochotica, was distributed. This extended 

 from northern Siberia southwestward to the Crimea, southeastward to 

 the Great Basin Sea, and southward along the shores of Asia through 

 Japan to New Zealand. 



In the Lower Jurassic we find a recurrence of the same conditions 

 that prevailed in the Karnic epoch, free communication through the 

 Central American and Asia Minor portals, and between the Pacific and 

 the Oriental Tethys, with nearly identical species ranging from the far 

 north to the south temperate region in Argentina, and from the Medi- 

 terranean eastward to Timor and westward to California. 



In the Middle Jurassic similar geographic relations continued, with 

 clear evidence of a warm climate from Franz Joseph Land to Madagascar 

 and Argentina, and no division into climatic zones. Cycads flourished 

 on the land, and corals built reefs in the seas. This was too good a 

 state of affairs to last long in this world, and there soon came a change. 

 The Central American portal was closed, as was that between the Pacific 

 and the Tethys. The Arctic Sea became the center of dispersion of a 

 boreal fauna, which made its way down to Eussia on one side, and to 

 California and Mexico on the other. This arrangement of the geo- 

 graphic provinces reminds us strongly of that during the Triassic epoch 

 of Pseudomonotis suh circularise and it continued into the Cretaceous 

 period. 



The Upper Cretaceous is signalized by the closing of the Bering 

 portal, and the wide distribution of a tropical fauna from the Indian 

 waters westward to the Mediterranean waters, and eastward through 

 Japan, around the North Pacific shore-line to California. This same 

 fauna was also distributed from the Mediterranean westward through 

 the Poseidon Sea to Mexico, and southward into South America. And 



