und on the northern and western coasts of
Ireland, in the Hebrides, in Scotland, and in North America. These are
no doubt the relics of an Arctic flora which flourished in high
latitudes in past times when the climate there was more temperate. A
list of these species will be found on page 166.

As none of them occur in Siberia, they must either have found their way
to North America and to Europe from the Arctic Regions, or have
travelled from North America across the latter to Europe. In any case a
former land-connection between the two continents must have existed.
This becomes the more evident when we examine the remarkable results
obtained by the late Professor Heer, who first described the Tertiary
plant-beds in North Greenland. No less than 282 species of plants have
been described by this eminent botanist from these deposits. A large
number of the plants found were trees belonging to the genus _Sequoia_,
_Thujopsis_, and _Salisburia_, besides beeches, oaks, planes, poplars,
limes, and magnolias. That they grew on the spot is proved by the
fruits, which have been obtained from these beds in various stages of
growth.

From a similar deposit in Spitsbergen a large number of fossil plants
have also been brought to light, many of which are identical with those
found in Greenland; and some of the Greenland forms (such as _Taxodium
distichum_ and _Sequoia Langsdorfii_) have been found too in Alaska,
showing that there was probably a continuity of land between Spitsbergen
and North America by way of Greenland. Two species of _Sequoias_,
namely, _S. sempervirens_ and _S. gigantea_, the well-known Californian
giant trees, are very closely allied to the Greenland forms discovered
by Professor Heer.

Heer assigned the Arctic plant-bearing beds to the Miocene epoch, but
doubts have been recently thrown upon this opinion by Mr. Starkie
Gardner, who brought forward arguments in support of his theory of their
being of the Eocene age. Professor Heer, however, was able to meet these
criticisms, and he is ably supported in his views by Professor Engler
and other eminent continental botanists.

It is evident that under the present conditions of temperature none of
those plants could have flourished in Greenland. The climate must have
been much milder than it is at present. Professor Heer estimated from
the general aspect of the fossil flora that the mean annual temperature
of North Greenland was at least nine degrees centigrade,