SUMMARY 



613 



to become the Dakota flora of the central Western States. This Dakota 

 flora undoubtedly spread southward to find its southernmost known limit 

 in Argentina. The pathway between these areas, although now largely 

 buried beneath later sediments, was undoubtedly open in Upper Cre- 

 taceous time. The presence in the Argentine "Dakota'' flora of a very 

 few elements of possibly later age may be sufficient to make it slightly 

 younger than the principal Dakota floras of the north — that is, it may 

 have taken an appreciable time for its journey, and it may not have 

 reached there until early Turonian time. 



A word may be said as to the possible, not to say probable, routes by 

 which the Triassic and Jurassic floras reached South America. It is 

 necessary to review briefly the plant distribution during Permo-Carbon- 

 iferous time in order to get a proper perspective. In Permo-Carbonifer- 

 ous time the world was divided into two phytogeographic provinces — a 

 northern and a southern — and there was extremely little commingling 

 of plant types between them. The southern province, characterized by 

 the so-called Glossopteris flora, embraced portions of India, Australasia, 

 South Africa, Antarctica, and eastern South America. It reached the 

 northern province at a single point in north central Eussia. It has been 

 found within 5 degrees of the South Pole. To my mind the facts all 

 point to the origin of this flora in the south, either in Australia or on the 

 Antarctic land-mass, and I believe there was in Permo-Carboniferous 

 time a practically continuous land connection between the Antarctic 

 Continent (Gondwana Land) and south Africa, Australia, India, and 

 South America. Any attempt to derive the Glossopteris flora of Brazil, 

 the Falkland Islands, and Buckley Island (85 degrees south) from the 

 north by way of North America is without supporting data. 



Some students — notably Bttingshausen — have held that the differences 

 between the northern and southern phytogeographic provinces that are so 

 marked in Permo-Carboniferous time continued Avell into the Jurassic. 

 This appears to be true only in part, for while there are some notable 

 differences in the floras of the two areas, the differences are by no means 

 so sharp as in Permo-Carboniferous time. For example, the Ginkgoales, 

 a dominant and widespread group of the north, did not reach the southern 

 province, and Podozamites, abundant in the north, is but sparsely repre- 

 sented in the south. From available data it appears that at least the 

 major portion of the early Mesozoic flora originated in the north, whence 

 they spread pretty much over the glol]e. Their routes of travel are not 

 always clear, however. It is possible tliat the Jurassic flora found on 

 Graham Land may liave reached this far soutlicrn ])()int by way of Nortli 



