412 MESEOSERE AND PALEOSERE. 



The equisetums and ferns doubtless constituted the characteristic consocies 

 of the seres, or at least of the hydrosere, leading to the above climaxes. This is 

 indicated by the evidence from the Triassic marshes of the Atlantic coast. 

 According to Chamberlin and Salisbury (1906 : 3 : 40) : 



"In favored portions of the Newark series from Connecticut to North 

 CaroUna, plant remains occur, and in the coal-beds of the latter State and of 

 Virginia, the flora is more amply represented. The Richmond coal-beds are 

 regarded by Fontaine as the products of marsh vegetation accumulating 

 where it grew, while the CaroUnian deposit shows more evidence of inwash, 

 and represents the vegetation of the adjacent country. The coal-beds of 

 Virginia contain immense numbers of equiseta and ferns, but almost no 

 conifers and but few cycadeans; the North Carolina deposits, comparatively 

 few ferns, but many conifers and cycadeans. As this distribution implies that 

 the conifers were not marsh plants, the pseudo-xerophytic pecuHarities of such 

 plants can not be appealed to in explanation of the markedly xerophytic aspect 

 of the Triassic conifers, as was done in the case of the Carboniferous trees." 



Jurassic succession. — As already indicated, the climate and vegetation of 

 the late Triassic continued into the Jurassic. A general cooUng of the climate 

 seems to have appeared in the transition from one period to the other, and this 

 doubtless had its effect in shaping the cUmatic zones, which are generally 

 recognized as occurring in the Jurassic. Neumayr (Schuchert, 1914 : 281) 

 reached the conclusion that the earth showed marked equatorial, temperate, 

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

 the same zones. His hypothesis was based upon the geographic belts of ammo- 

 nite distribution, which are now regarded as indicative of faunal realms and 

 not of temperature belts. StiU, it is admitted that there were clearly marked 

 temperature zones during the Jurassic, a warmer one, including the present 

 tropical and temperate zones, and a cooler polar zone. To this differentiation 

 of climate must have corresponded a division of North American vegetation 

 into climaxes. Moreover, the temperature belts must have been marked by 

 interior areas of greater or less aridity, such as seem to have occiured in the 

 Great Plains region. Thus, as in the Triassic, it seems probable that there 

 were three great cUmax regions in North America, namely, a broad-leaved 

 gymnosperm, a needle-leaved or scale-leaved gymnosperm, and a cycadean 

 climax. The first consisted of ginkgos and araucarians perhaps, the second of 

 pines, sequoias, etc. It seems not improbable that there was a further differ- 

 entiation of climax formations, similar to that of to-day, within each of these 

 great climatic regions. Angiosperms had not yet appeared, and the important 

 successional dominants must still have been equiseta and ferns, and in addition, 

 perhaps, dwarf or shrubby forms of the dominant gymnosperms. The appear- 

 ance of zones, or the renewed emphasis of existing ones, produced a potential 

 clisere, which may have shifted somewhat northward in the warmer Middle 

 Jm-assic, and southward again in the somewhat cooler Upper Jiu-assic (plate 

 60, A, b). 



The general floral conditions in North America durii^ the Jurassic are 

 summed up by Knowlton (1910:109). 



"The flora of the Jurassic, while in the main a continuation of that of the 

 late Trias, and consisting of equisetimas, ferns, cycads, ginkgos, and conifers, 

 shows the incoming of a number of more modern types in those groups. The 



