MESOZOIC AND TERTIARY FLORAS 201 



Arizona, and a very few species from Plumas County, California. 

 Going southward we have small collections from Sonora, from about 

 the City of Mexico, in Honduras, Chile, and western Argentina. In 

 other parts of the world Triassic floras have been found in England, 

 east coast of Greenland, Spitzbergen, North Germany, southern 

 Sweden, Italy, southwestern Spain, Persia, India, China, Tonkin, 

 Japan, New South Wales, New Zealand, and South Africa. 



What, now, are the characters of the Triassic flora ? The domi- 

 nant types of the Paleozoic have largely disappeared. The Lepido- 

 dendrae, Sigillariae, Calamites, Cordaites, Sphenophyllae, and 

 Cycadofilices, so far as ascertained, have all gone, as well as a num- 

 ber of important genera of ferns — Cheilanthites, Mario pteris, Megalop- 

 teris, etc. The most notable survival from the Paleozoic is the 

 so-called Glossopteris flora, which has been found with a few associated 

 forms in Rhaetic rocks at Tonkin, the Stormberg series of South 

 Africa, New South Wales, etc. 



The Triassic flora consists essentially of equisetums, ferns, cycads, 

 and conifers of many genera. A few forms such as Ginkgo, Cla- 

 dophlebis, Thinnjeldia, etc., had a small beginning in the Paleozoic 

 and expanded in the Mesozoic into large groups. But most of the 

 flora is of distinctly Mesozoic and northern origin. 



It has often been said that the plants of the Triassic are depau- 

 perate and pinched in aspect, indicating unfavorable climatic con- 

 ditions. The paleobotanical facts do not altogether bear this out. 

 In North Carolina, Virginia, and Arizona, there are trunks of trees 

 preserved, some of which are 8 feet in diameter and at least 120 feet 

 long, while hundreds are from 2 to 4 feet in diameter. Many of the 

 ferns are of large size, indicating luxuriant growth, while Equisetum 

 stems 4 to 5 inches in diameter are only approached by a single 

 living South American species. The cycads are not more depau- 

 perate than those of subsequent horizons, nor do they compare 

 unfavorably with the living representatives. 



The complete, or nearly complete absence of rings in the tree 

 trunks indicate that there were no, or but slight, seasonal changes 

 due to alternations of hot and cold, or wet and dry periods. The 

 accumulations of coal — in the Virginia area aggregating 30 to 40 

 feet in thickness — indicate long-continued swamp or marsh condi- 



