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THE STORY TOLD BY FOSSIL PLANTS

Lower Cretaceous plants are found in the rocks of all the continents, and they are particularly abundant in North America and Europe. The two most extensive Lower Cretaceous floras are those preserved in the Potomac group of rocks of Maryland and Virginia and those of the rocks of the opposite side of the Atlantic, in southern Portugal. Comparisons of these floras shed light on the place of origin and the migrations of the various types. A third large

Fig. 8.—Restoration of Wielandiella, one of the best known branched cycads of the older Mesozoic. (After Nathorst.)

Lower Cretaceous flora is that of the so-called Wealden of England, Belgium, and Germany. Other floras of this age are found in South Africa and eastern Asia, as well as in Spitzbergen, Australia, New Zealand, and Greenland. Although the known floras of the Lower Cretaceous epoch necessarily represent only a small percentage of the species that clothed the earth during that time, they furnish some suggestive data concerning the march of vegetation during

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