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F. H. KNOWLTON 



tions, while the presence of ferns, some of them tree-ferns, indicate 

 on the whole a moist, warm, probably at least sub-tropical climate. 



Jurassic. — Coming, now, to the Jurassic, we find in the lower 

 portion indications of a continuation of conditions which obtained in 

 the upper portions of the Trias. The distinctive Paleozoic elements 

 had finally disappeared, and the Mesozoic life-forms were in full 

 swing, expanding in the middle and upper parts of the period into 

 the abundant and widespread flora as we know it. In fact the 

 relative uniformity and wide extension of the Middle and Upper 

 Jurassic flora is one of the most interesting and impressive exhibits 

 that we have. (See map showing approximate distribution of Triassic 

 and Jurassic flora.) 



There is no paleobotanical evidence indicating the presence of 

 the Jurassic in Eastern North America. In the western interior 

 Jurassic plant-bearing beds occur in the Black Hills, South Dakota, 

 and the Freezeout Hills, Carbon County, Wyoming. We then pass 

 to the Pacific coast, where we have a fine flora near Oroville, Cali- 

 fornia; also northward in Trinity and Tehama counties, California, 

 and Douglas and Curry counties, Oregon. 



The following is an outline of the world distribution of the flora : 



