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POPULAR SCIENCE REVIEW. 
the Oligocene period we have proofs of the commencement of 
that series of volcanic outbursts which attained their climax in 
the succeeding period of the Miocene. But along the great 
Alpine axis movements on a grander scale were taking place, 
which resulted in the formation of vast lakes, in which great 
thicknesses of strata were accumulated; these lakes being 
sometimes, by the action of the subterranean forces, placed in 
communication with the open ocean. At the end of the period 
the elevatory forces so far prevailed over those producing 
subsidence, that the whole area was converted into a great 
continent, which remained above water during the Miocene but 
was to some extent submerged in the Pliocene and re-elevated 
in the recent period. Such appears to he the succession of 
changes in the physical geography of this part of the Earth’s 
surface during the several Tertiary epochs. 
It is a very interesting circumstance, as I have pointed out 
in a memoir recently laid before the Geological Society of 
London, that we have in the Hampshire Basin very beautiful 
and interesting representatives of at least the Middle and Lower 
divisions of the Oligocene system. Owing to an unfortunate 
error in determining the order of succession of these beds, their 
thickness has been hitherto greatly under-estimated, and they 
have been grouped with the Eocene by some authors and 
divided between the Eocene and the Miocene systems by 
others. Ho fact, however, can be more certain than that those 
fluvio-marine strata of the Isle of Wight and the Hew Forest 
are the representatives of the great Oligocene system of the 
Continent. The new classification which is now proposed for 
them is as follows : — 
Oligocen j Wanting in the British Islands. 
Middle ( Hempstead Series (marine and estuarine), 100 feet. 
Oligocene. ( Bemhridge Group (estuarine), 300 feet. 
Lower ( Brockenhurst Series (marine), 25 to 100 feet. 
Oligocene. ( Headon Group (estuarine), 400 feet. 
Whether we study the marine mollusca, the fresh- water and 
terrestrial testacea, the reptilian and mammalian fauna, or the 
terrestrial flora of the period, we find the most convincing 
proofs that these strata of the Hampshire Basin are the exact 
equivalents of that great system of strata which has received 
the name of the Oligocene upon the Continent, which, as we 
have seen, attains to such enormous thickness and importance 
in some areas, and which everywhere is so well characterized 
by the distinct assemblage of fossils which it contains. 
It is a remarkable circumstance that nearly all the great 
