44 Origin of the British Flora. 
borne out by the evidence above mentioned. We have no 
indication in our Tertiary or later deposits of a number of 
alternating Glacial and Interglacial Epochs, such as are 
required on the theory of Croll* adopted by Professor 
James Geikie.f On the other hand, the evidence is 
perfectly clear that this country saw two cold Epochs, and 
certain indications make one suspect that there may have 
been a third, less rigorous. The exact succession of events 
is at present very difficult to follow; for it is unsafe to 
compare isolated records, which belong to different regions, 
and may not belong to the same period. We need more 
excavation and close examination of localities such as 
Hoxne and the Selsey Peninsula, where several stages can 
be studied in chronological order, with no possibility of 
mistakes in the succession. 
The wind-borne ‘loess’ of Central Europe, with its. 
desert or sand-dune mollusca and mammals, belongs 
apparently to the second cold period just alluded to. 
Only slight indications of this dry climate have been 
discovered in Britain, and, though it may have marked an 
important stage in the building up of our flora, we know 
little about its plants in the south, while nearer the glaciated 
area those found are common Arctic forms. It is always 
difficult to obtain botanical evidence of a bygone period 
of drought, for desert-plants seldom find their way into 
lacustrine deposits, and porous sub-aerial deposits like 
drift-sand or loess are the worst possible for the preserva- 
tion of plant-remains, though they may be full of calcareous 
fossils. 
The South of England during the second period of 
glaciation seems to have suffered from dry cold winters, 
which froze the ground unprotected by snow, and allowed 
the summer rains to fall on soils rendered impervious by 
* Climate and Time. t+ Great Ice Age. 
