IO THE SCOTTISH BOTANICAL REVIEW 
to the tropics, or a peculiarly wide distribution during such 
phases. Suess believes that the negative phases were more 
or less spasmodic in character, such as might lay bare in 
short periods, geologically speaking, wide areas of the marine 
platforms of the continental shelves. In certain cases the 
result of such changes in geography would be to remove 
the higher ground to a distance from warm ocean currents, 
where its influence on atmospheric precipitation would be 
lessened. Very rich fossil floras and abundant deposits of 
coal are of more frequent occurrence in rocks interdigitated 
with marine deposits in the positive phases, in a manner 
suggestive of the deltaic deposits of rivers draining areas of 
great rainfall. Each successive phase shows marked accession 
in new forms belonging to more highly evoluted groups of 
plants, and extinction of older types. We may infer that 
the gradual reduction of continental areas, induced by the 
marine transgressions, was accompanied by increase in 
areas subject to a humid climate at the expense of arid 
regions. 
3. From glaciation, large areas of the earth’s surface under- 
going sterilisation under ice sheets, with further changes in 
the vegetation of the surrounding areas from change of 
climate. On the melting of the ice sheet the whole area is 
transformed. The soils of wons have been removed, the 
nature of the topography has been altered, and various 
peculiar sterilised deposits have been plastered over the 
surface. The recently glaciated regions of Europe and 
North America exhibit large areas of peat bogs and plant 
formations, showing a close historical relation to the results 
of glaciation. More,extensive areas are believed to have 
undergone glaciation in Permo-Carboniferous times, in an 
extinct continental region known as Gondwanaland, com- 
prising parts of India and Australia, a large area of Africa, 
and land then existing in the present site of the Indian 
Ocean (8). The Permo- Carboniferous conglomerates of 
Australia, Africa, and India are immediately succeeded by 
a sequence of deposits containing a fossil flora of fern-like 
plants, the Glossopteris flora peculiar to this region and to parts 
of South America. It has been suggested that the appearance 
of this flora was due to the severity of the climate (11). 
