CONIFERS OF THE MESOZOIC PERIOD. 99 



formations have been classed as belonging to the Age of Cycads.* In 

 the succeeding system, the Jurassic, consisting of beds of argillaceous 

 limestones, marls and clays termed Lias and Oolite, the vegetation so far 

 as it is known to us was essentially Gymnospermous. The prevalent 

 trees of the forest were Cycads, but associated with them were primeval 

 forms of Araucaria, Thuia and Pin us. Phyllostrobus found in the 

 Kimeridge Clay of Orbagnoux and Palseocyparis are, according to Solms- 

 Laubach, the oldest known progenitors of the Cypress tribe. Ancestral 

 forms of Taxacese also appear distinctly in the Jurassic period of which 

 the best known is B'aiera, a genus allied to Gingko, scarcely exceeding 

 the existing species in size. In the Cretaceous system the earliest known 

 progenitors of the abundant dicotyledonous trees of the present day 

 appear ; they were allied to the Oaks, Beeches, Walnuts and Tulip-trees 

 of our flora, and with them were associated numerous Conifers which 

 spread far into the Arctic regions. In the Cenomanian beds appear the 

 earliest forms of Pinus that can be satisfactorily identified as such ; an 

 earlier form has been found in the Rhsetic beds of the upper Triassic 

 formation, but it is not absolutely free from doubt. All the Pine cones 

 found in the Mesozoic Age belong to the Cembra and Strobus sections 

 of the existing Pines ; the scales of the cones are without an apophysis 

 or thickening at their apical end. The most common Conifers of the 

 upper Cretaceous period were the ancestors of the gigantic Sequoias of 

 California ; cones of these are abundant and are sometimes attached to 

 their branches with foliage which agrees closely with that of the existing 

 species. 



Different phases of plant life appear as we enter upon the Tertiary 

 or Cainozoic (Recent Life) Division. The transition from the later 

 Mesozoic to the earlier Cainozoic formations was marked by great 

 geographical changes in Western Europe which must have occupied a 

 vast period of time. The fossil remains^of plants found in the Eocene 

 or lowermost of the Tertiary system of rocks indicate that the age of 

 Lycopods, Ferns and Yew-like Conifers had passed away, and that the 

 threshold of modern types of life had been reached. Ancestral forms of 

 dicotyledonous trees both evergreen and deciduous were taking their 

 place. One of the most striking phenomena of the Tertiary period is 

 the remarkable change in climate which the northern hemisphere of the 

 globe underwent. "At the beginning it was of a tropical or sub-tropical 

 character, even in the centre of Europe and North America. It then 

 gradually became more temperate, but flowering plants and shrubs 

 continued to live even far within the Arctic Circle where then, as 

 now, there must have been six sunless months every year. Growing 

 still milder the climate passed eventually into a phase .of extreme cold 

 when snow and ice extended from the Arctic regions into the centre of 

 Europe and Xorth America. Since that time the cold has again 

 diminished until the present thermal distribution has been reached."! 

 Abundant evidences of these climatic changes present themselves in the 

 fossil remains distributed over the great area affected by them. Trees 

 allied to the gigantic Sequoias of California, the Gingko, Thuias and 

 other Cupressinese flourished in Xorth Greenland ; Spruce Firs, Pines and 

 Cypresses in Spitzbergen. In Great Britain during Eocene times, 

 Cypress-like trees allied to the Australian genus Callitris were frequent ; 

 remains of a Libocedrus, much like the L. dei-urrem of California, have 

 * Sir A. Geikie, Text Book of Geology, p. 837. t Idem, p. 761. 



