The Meeting of the British Association. 
1 7i 
no trace, and many of which have almost certainly been lost for ever. 
In the Upper Carboniferous and Permian epoch we come to an ex¬ 
tremely rich flora consisting of Pteridophytes, Cycadofilices and 
Gymnosperms, which are fortunately sometimes preserved in such 
a way that their anatomical structure can he investigated. Here 
also we meet with the extremely interesting fact of the existence of 
two types of vegetation—a northern and a southern (the so-called 
Glossoptcris-fiova.), which in some areas (e.g. Northern Russia, 
South Africa and Brazil) overlap, but contain for the most part 
distinct forms. It is probable that while most of the preserved 
remains of the northern type represent a luxuriant salt-lagoon 
vegetation, the southern type lived under arctic conditions, as 
evidenced by the association of the plant-remains with glacial 
boulder-beds, resting on glaciated rocks. It is probable that this 
state of things originated by the uniform Devonian and lower 
Carboniferous flora continuing to flourish in the north, some of its 
characteristic types being succeeded by new ones, while in the 
south arctic conditions came to prevail over the huge continental 
area (the so-called Gondwana Land) of which the present land of 
the southern hemisphere forms but isolated relics. On this 
continent the Glossopteris-fi ora originated, and in later Permian 
and Triassic times “ pushed northward over a portion of the area 
previously occupied by the northern flora.” 
“ During the Triassic period the vegetation of the world 
gradually changed its character; the balance of power was shifted 
from the Vascular Cryptogams, the dominant group of the Palaeo¬ 
zoic era, to the Gymnosperms.” The records are comparatively 
poor, but there is evidence that while the northern flora was thus 
changing its character very much, the Glossopteris -type persisted in 
the southern hemisphere. 
The Rhaetic flora, on the other hand, shows “ an almost world¬ 
wide range of a vegetation of uniform character. . . . Gymnosperms 
have ousted Vascular Cryptogams from their position of superiority ; 
ferns indeed are still very abundant, but they have undergone many 
and striking changes, notably in the much smaller representation 
of the Marattiaceae. The Palaeozoic Lycopods and Calamites 
have gone, and in their place we have a wealth of Cycadean and 
Coniferous types.” This new type of vegetation extends with 
striking uniformity right up to the Wealden (lower Cretaceous) 
epoch. 
The Cycadophyta of this great Mesozoic flora are extremely 
