72 On the Origin and Distribution of the British Flora.
Proteaceae and Leguminosae. At La Louviere,7 in Hainault, in
clays belonging to the period of the Gault, is a flora consisting
of conifers and cycads, like those of Kome and Folkestone;
whilst at Aix-la-Chapelle,8 in sands of Upper Chalk age,
we have a far different assemblage of plants, including,
with the ferns, Asplenium, Lygodium and Gleichenia; with
Sequoia and other conifers, species of screw-pine and nume-
rous Preteaceae (amounting to nearly 70 species out of 200),
some belonging to such genera as Banksia, Dryandra and
Leucospermum, which are now confined to Australia and the
Cape. With these are Eucalyptus, fig, bog-myrtle, willow,
poplar, oak, and beech. In the lignites of the Dakotah group,9
on the plains of Eastern Kansas and Nebraska, a remarkable
flora has been discovered, embracing such forms as poplar,
willow, birch, oak, bay, cinnamon, liquidambar, magnolia,
tulip-tree, maple, and plum ; and in New Zealand,10 in beds
also of Cretaceous age, we have the beech, with many repre-
sentatives of the Myrtaceae, and of genera still existing in
that country. Professor Lesquereux is of opinion11 that the
existing arborescent flora of North America originated in the
Dakotah group, and subsequently migrated to Europe. In the
London clay, at Sheppey, we have fruits of Proteaceous
7 Coemans, 'Mem. de l'Acad. roy. de Belgique,' tome xxxvi.
8 Lyell, 'Student's Elements of Geology,' 1st ed., p. 278, Morris, op. cit.,
pp. 49—51, and the numerous papers there quoted.
9 Admirably described and discussed by Professor Lesquereux, 'The
Cretaceous Flora,' Washington, 1874.
10 Dr. Hector, 'Trans. New Zealand Institute,' vols. ii. and vi.
11 Op. cit., and 'Geol. Survey of Montana,' 1871, p. 314. Note also
Mr. De Rance's remarks in the geological appendix to Sir George Nares'
'Narrative of a Voyage to the Polar Sea':—" In the overlying American
Eocenes occur types of plants occurring in the European Miocenes and
still living, proving the truth of Professor Lesquereux's postulate that the
plant types appear in America a stage in advance of their advent in
Europe. These plants point to a far higher mean temperature than those
of the Dakotah group." "This," adds Mr. A. E. Wallace (' Island Life,'
p. 183), "is very important as adding further proof to the view that the
climates of former periods are not due to any general refrigeration, but to
causes which were subject to change and alternation in former ages
as now."