9 STRUCTURAL AND FIELD GEOLOGY 
examples may be cited. Certain relatively recent accumula- 
tions of calcareous tufa, occurring at La Celle near Paris, 
have yielded well-marked remains of the Canary laurel 
(Laurus Canartensis). There is no doubt, therefore, that 
this plant formerly flourished in Northern France. It is no 
longer a native of that country, however, its headquarters 
being in the Canary Islands, where it is found flourishing 
luxuriantly in the woody regions with a northern exposure, 
between a height of 1600 feet and 4800 feet above the sea— 
regions which are nearly always enveloped in steaming 
vapours, and exposed to the heavy rains of winter. The 
temperature there keeps above 69° F. during the greater part 
of the year, rarely falling in the winter months below 59° or 
60°, and only on the coldest days reaching 49°. The presence, 
therefore, of this variety of laurel in the Pleistocene tufa of 
‘La Celle shows that the winter climate of Northern France 
must formerly have been very mild. The laurel in question 
is most susceptible to cold, and as it flowers in the winter 
season, it is obvious that repeated frosts, such as are now 
experienced in the north of France, would prevent it repro- 
ducing its kind. Another and more familiar example of the 
important evidence which is sometimes afforded by fossil 
remains of existing types is that of the Polar willow (Salx 
polaris)—a characteristic arctic plant, living in Northern 
Lapland, Spitzbergen, etc. This dwarf willow has been met 
with again and again in Pleistocene deposits in Southern 
Sweden, Denmark, England, etc., and in various parts of 
Central Europe, as far south as Bavaria and the low-lying 
parts of Switzerland. It cannot be doubted, therefore, that 
the appearance of the Polar willow so far south of its present 
habitat, points to a very considerable climatic change—arctic 
conditions would seem to have prevailed at a relatively recent 
period in what are now the temperate latitudes of our 
continent. 
It is obvious, however, that the evidence of fossils as to 
climatic conditions must be much stronger when a whole 
assemblage of organic remains tells the same tale. In the 
case of the tufa of La Celle, for example, the Canary laurel 
is accompanied by the remains of many other plants, as 
well as by shells of land-snails, each of which is indicative 

