CLIMATES OF GEOLOGIC TIME. 281 



In the Liassic there are now known 415 species of insects that remind one much of 

 modern forms. Nearly all were dwarf species, smaller than similar living insects of the same 

 latitude and far smaller than Paleozoic or Upper Jurassic insects. Handlirsch (1910b) 

 is positive that this uniform dwarfing of the Liassic insects was due to a general reduction 

 of the climate and that the temperature was then cool and like that of present northern 

 Europe between latitudes 46° and 55°. The climate, he states, was certainly cooler than 

 either that of the Middle Triassic or Upper Jurassic. 



In this connection we must not overlook the fact that the known Liassic insects are of 

 wide distribution, for 172 species are known from England, 164 from Mecklenburg, northern 

 Germany, 75 from Switzerland, and 2 from upper Austria. With this depauperating of 

 the insects and the vanishing of the late Triassic ammonites, there is also to be noted a 

 marked ciuantitative reduction and geographic restriction among the reef corals of Liassic 

 time We therefore are seemingly warranted in concluding that the cooling of the climate 

 in late Triassic and early Jurassic time was not local in character, but was rather of a 

 general nature. Much workable coal was also laid down in Liassic time, not only in Hun- 

 gary but also in many places eastward into China and Japan. In addition, the many black 

 shales of this time furnished further evidence of cool and non-tropical chmates; coal and 

 black shales are so general in occui-rence throughout the Liassic rocks that the time is often 

 referred to as the Black Jura. Finally, certain Liassic conglomerates of Scotland have been 

 thought by some to be of glacial origin (J. Geikie). 



Jurassic. — The Jurassic formations of Europe are so rich in fossils that they have 

 been the classic ground on which many paleontologists and stratigraphers were reared. 

 From the studies of these faunas came the first clear ideas of climatic zones and world 

 paleogeographic maps through the work of the great Neumayr of Vienna. As the result 

 of a very long study of the ammonites and their geographic distribution, he came to the 

 conclusion in 1883 that the earth in Jurassic time had clearly marked equatorial, temperate, 

 and cool polar climates, agreeing in the main with the present occurrence of the same 

 zones. He also said that "the equator and poles could not have very much altered their 

 present position since Jurassic times." His conclusions were, however, assailed by many, 

 and while no one has greatly altered his geographic belts of ammonite distribution, still 

 the consensus of opinion to-day is that these are representative rather of faunal realms 

 than of temperature belts. On the other hand, it is admitted that there were then clearly 

 marked temperature zones — that is, a very wide medial warm-water area, embracing the 

 present equatorial and temperate zones, with cooler but not cold water in the polar areas. 

 That the oceanic waters of Middle and (somewhat less so) of Upper Jurassic times were 

 warm throughout the greater part of the world is seen not only in the very great abundance 

 of marine life — probably not less than 15,000 species are known in the Jurassic — but also 

 in the far northern distribution of many ammonites, reef corals, and marine saurians. 

 The Jurassic often abounds in reefs made by sponges, corals, and bryozoans. Jurassic corals 

 occur 3,000 miles north of their present habitats. 



The Jurassic floras were truly cosmopoHtan, and Knowlton tells us that of the North 

 American species, excluding the cycad trunks, about half are also found in Japan, Man- 

 churia, Siberia, Spitzbergen, Scandinavia, or England. "What is even more remarkable, 

 the plants found in Louis Phihppe Land, 63° S., are practically the same [both generically 

 and specifically] as those of Yorkshire, England. * * * The presence of luxuriant ferns, 

 many of them tree ferns, equisetums of large size, conifers, the descendants of which are 

 now found in southern lands, all point to a moist, warm, probably subtropical climate" 

 (1910a: 204-5). The insects of this time were again large and abundant, indicating a 

 warm climate — evidence in harmony with the plants. 



At the close of the Jurassic the Sierra Nevadas of California and the Humboldt Ranges 

 of Nevada were elevated; probably also the Cascade and Klamath Mountains farther north; 



