300 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
were, however, assailed by many, and while no one has greatly 
altered his geographic belts of ammonite distribution, still the con- 
sensus of opimion 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 cosmopolitan, and Knowlton tells us 
that of the North American species, excluding the cycad trunks, 
about half are also found in Japan, Manchuria, Siberia, Spitzbergen, 
Scandinavia, or England. ‘‘What is even more remarkable, the, 
plants found in Louis Philippe Land, 63° S., are practically the 
same [both generically and specifically] as those of Yorkshire, Eng- 
land. * * * 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’’ (1910). 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; but this disturbance 
seemingly had no marked effect upon the world’s climate, though 
there was a considerable retreat of the seas from the continents. 
Cretacic.—The emergence of the continents at the close of the 
Upper Jurassic gave rise to extensive accumulations of fresh-water 
deposits, known in western Europe as the Wealden, and in the Rocky 
Mountain area of North America as the Morrison. These are now 
regarded as of Lower Cretacic (more accurately Comanchic) age. 
Along the Atlantic border of the United States occur other conti- 
nental deposits, known as the Potomac formations, in the upper 
part of which the modern floras or Angiosperms make their first 
appearance. Before the close of the Lower Cretacic this early hard- 
wood forest had spread to Alaska and Greenland, where elms, oaks, 
maples, and magnolias occurred. Knowlton concludes from this 
evidence that the climate “was certainly much milder than at the 
present time’? and ‘was at least what we would now call warm 
