the maidenhair tree — seward 449 



shores of a large gulf occupying the site of the southern part of the 

 present river's course. These fossil leaves, superficially indistinguish- 

 able from the foliage of the living tree, with many others from Tertiary 

 rocks, are usually spoken of as Ginkgo adiantoides. Specimens have 

 been obtained from rocks belonging to all stages of the Tertiary era, 

 particularly from the earlier or Eocene strata. Some of the most 

 beautifully preserved leaves are from the Island of Mull, where they 

 were collected many years ago from sedimentary deposits associated 

 with the horizontal sheets of basalt which give the characteristic 

 terraced profile to some of the Inner Hebrides. In the early days of 

 the Tertiary period, subsequent to the upheaval of the floor of the 

 Cretaceous sea, volcanic forces, which had long been dormant, broke 

 out into activity on a stupendous scale: through fissures in the 

 earth's crust and from volcanoes sheets of lava spread over an enor- 

 mous area including northeast Ireland, the Inner Hebrides, the 

 Faroes, Greenland, and other arctic regions. The columnar basalts 

 of the Giant's Causeway in northern Ireland and FingaPs Cave in the 

 island of Staffa belong to this Tertiary lava-field. The occasional 

 occurrence of water-borne sedimentary material intercalated among 

 the sheets of lava, as in the Island of Mull at Ardtun Head on the 

 southwest coast, bears witness to periods of quiescence during which 

 forests were able to colonize the lava-fields. Ginkgo was one of the 

 forest trees. The leaves were first described by the late Mr. Starkie 

 Gardner about 50 years ago, who spoke of them as indistinguishable 

 from those of the living tree. Realizing that plants as old as the 

 Eocene stage of the Tertiary period — a stage separated from the 

 present by perhaps 80 million years — were probably not specifically 

 identical with those of the present day, he referred the Mull fossils 

 to the Tertiary species Ginkgo adiantoides. A recent examination of 

 the epidermal cells of the Mull leaves by Dr. Florin of Stockholm 

 revealed certain peculiarities which led him to rename the species 

 G. gardneri. We do not know anything of the "flowers" of this 

 species; but it is safe to assert that the Mull tree was very closely 

 allied to G. biloba. 



Since the discovery of fossil Ginkgo leaves in Tertiary rocks of 

 northern Italy, nearly a hundred years ago, numerous specimens 

 from Eocene and later rocks have been described from widely separated 

 localities in arctic and temperate regions. The significant fact that 

 emerges from a review of the evidence furnished by rocks of the 

 Tertiary period is that species of Ginkgo, how many we do not know, 

 had a far-flung geographical range: the genus was represented in 

 forests from the Pacific coast of North America to Alaska and arctic 

 Canada; in western and eastern Greenland as far north as latitude 

 74°, where leaves have been found in Tertiary rocks of Sabine Island. 

 With many other trees Ginkgo flourished in Spitsbergen, in the forests 



