October 8, 1903] 



NATURE 



561 



difference between northern and southern floras, a feature 

 not shown either by the preceding Devonian and Lower 

 Carboniferous or by the succeeding Lower Mesozoic floras? 

 In Brazil, Prof. Zeiller has recorded the occurrence of a 

 flora including Lepidophloios, a well-known European 

 member of the Lycopods, associated with such characteristic 

 southern types as Gangamopteris and Noeggerathiopsis. 

 Similarly from the Transvaal a European species of 

 Sigillaria, with a Lepidodendroid plant, and another 

 northern genus, Psygmophyllum, have been found in beds 

 containing Glossopteris, Gangamopteris, Noeggerathiopsis, 

 Neuropteridium, and other members of the so-called Glosso- 

 pteris flora. In India, the Glossopteris flora exhibits an 

 entire absence of Lepidodendron, Calamites, Sigillaria, and 

 other common northern genera, while Sphenophyllum is re- 

 presented by a single species. The Australian Permo- 

 Carboniferous flora is also characterised by the absence of 

 the great majority of the northern types. Until a few years 

 _:o the genus Glossopteris had not been discovered in 



between the two provinces into which the Permo-Carbon- 

 iferous vegetation was divided. As regards an explanation 

 of this fact, we can only hazard a guess ; as Dr. Blanford 

 and others have pointed out, there is a probable solution 

 to hand. Briefly stated, the Upper Palaeozoic plant-bearing 

 strata of India, South America, Australia, and South Africa 

 are in close association with boulder-beds of consider- 

 ably extent. In some places, as for example in India and 

 Australia, the boulder-beds rest on rocks bearing un- 

 mistakable signs of the grinding action of ice. There can 

 be no reasonable doubt that the huge continental area of 

 which India, South Africa, parts of South America, and 

 Australia remain as comparatively insignificant remnants, 

 was exposed to climatal conditions favourable to the 

 accumulation of snow and to the formation of glaciers. 

 One possible explanation, therefore, of the existence of a 

 distinct vegetation in the southern area is that the climate 

 was such as to render impossible the existence of those 

 coal-forest plants that exhibited so vigorous a development 



Map II. — Permo-CarboniferoQs Floras. 



r.::.-"-y.a =■ aiossoptens (Southern Flora). 

 ^■■1 = Northern Flora. 



Europe, but in 1897 Prof. Amalitzky recorded the occurrence 

 of this genus in association with Gangamopteris in Permian 

 rata in northern Russia. 



We see, then, that in Brazil and South Africa the Glosso- 

 yi'us flora and the northern flora overlapped, but the 

 former was the dominant partner. On the other hand, in 

 rocks belonging to a somewhat higher horizon in Russia, 

 we meet with a northern extension of the Glossopteris flora. 

 Map II. serves better than a detailed description to illustrate 

 the geographical distribution of these two types of vegeta- 

 tion in the Permo-Carboniferous era. 



There is little doubt that the differences between the flora 



of the southern continent, that existed towards the close of 



»hp Carboniferous and during the succeeding Permian 



t iod, and that which flourished farther north have in some 



-pects been exaggerated ; geographical separation has 



ived too conspicuous a part in influencing botanical 



menclature. Granting the existence of identical genera 



, representative types, there remains a striking difference 



NO. 1 77 1, VOL. 68] 



in northern latitudes. There is, moreover, another consider- 

 ation, and that is the effect on the vegetation of an enormous 

 continental mass ; in North America and Europe it is prob- 

 able that the forests grew on low-lying land penetrated by 

 lagoons and in part submerged under shallow brackish 

 water, a disposition of land and sea very different from that 

 in the so-called Gondwana Land of the South. Possibly 

 the apparently uniform vegetation of the Devonian and 

 Lower Carboniferous period was unable, through stress of 

 climatal conditions, to prolong its existence in the southern 

 area, while in the north it continued to flourish, and as the 

 evolution of new types proceeded in rapid succession it was 

 not slow to colonise new areas stretching in South America 

 and South Africa to the confines of the Glossopteris flora. 



There seems good reason for assuming that the Glosso- 

 pteris flora originated in the South and before the close 

 of the Permian period, as well as in the succeeding Triassic 

 era, pushed northward over a portion of the area previously 

 occupied by the northern flora. This northward extension 



