128 MIOCENE CLIMATE. 



time, we shall acquire important data as to the climate of the 

 Tertiary district. Upon these points we obtain evidence by 

 submitting- to a careful examination the plants and insects lying- 

 together upon the same slab of stone. If these are well pre- 

 served and lie exactly in the same plane of bedding, they must 

 have been simultaneously enveloped by the stony mass. We 

 should, however, take into consideration that only such objects 

 have come down to us as were enclosed by the stone in a short 

 time, while those which lay longer in the water became decom- 

 posed and perished. An exact comparison of many slabs from 

 (Eningen and the Schrotzburg has proved that in Miocene 

 times the periodical phenomena of the vegetable world were of 

 the same nature as those now going on in the subtropical zones. 

 On a slab of stone from the Schrotzburg the flower of the cam- 

 phor-tree lies quite close to the male flowers of a willow (Salix 

 varians] y and very near to leaves of the plane, the liquidambar, 

 and the maple. The willow and camphor-trees consequently 

 bloomed at the same time; the planes already unfolded their 

 leaves, and were likewise in flower; and it appears that at the 

 same time the poplars flowered, for upon another slab Prof. 

 Heer has seen associated with the male catkins of the poplar 

 (Populus latior) the leaves of planes, elms, liquidambars, and 

 willows. This is a condition of things which no longer occurs 

 in Switzerland, or indeed anywhere in the temperate zone. The 

 willow above referred to is most nearly allied to the crack- 

 willow (Salix fragilis), which flowers in Central Europe at the 

 end of April and the beginning of May; the development of 

 the leaves and flowers of the plane takes place later. Until 

 towards the middle of May the plane remains perfectly bare ; 

 then the buds begin to open, the leaves break forth very gra- 

 dually, and simultaneously with them appear the globular cat- 

 kins ; but it is only towards the end of May that the plane 

 acquires its green mantle and comes into full bloom, and it is 

 some time longer before it arrives at its perfect foliage. At the 

 time when the crack-willow begins to flower, the planes are 

 therefore quite bare in Switzerland, and three or four weeks 

 elapse before they bear fully developed leaves. If we assume 

 that the flowering of the willow lasts fourteen days, there is still 

 an interval of one or two weeks between the fall of its flowers 



