28 A SUMMER IN GREENLAND 



Gleichema) living to-day in tropical and sub- 

 tropical countries ; there are also twigs of Conifers, 

 some of which are almost identical with those of 

 the Mammoth tree (Sequoia (Wellingtonia) gigan- 

 fea now confined to a narrow strip of the Cali- 

 fornian coast), and massive stems of forest trees. 

 None of the leaves preserved in the Greenland 

 rocks have a greater fascination for the student of 

 the past history of living plants than those of the 

 genus Ginkgo. This genus is now represented by a 

 single species, the Maidenhair tree (Ginkgo biloba\ 

 which is sometimes said to occur in a wild state in 

 China, though it is probable that even in China 

 and Japan, where it grows abundantly, it is only 

 as a cultivated tree associated in the oriental mind 

 with some religious symbolism. Ginkgo is often 

 planted in gardens and parks in Europe and 

 America and is distinguished from all other trees 

 by its broad and often lobed, wedge-shaped leaves. 

 Fossil leaves, some indistinguishable from those 

 of the sole survivor of this ancient genus, have 

 been found in the Cretaceous sediments on Uper- 

 nivik Island (Map 5), in sedimentary rocks asso- 

 ciated with basaltic lavas at Sabine Island (lat. 

 75 N.) on the east coast of Greenland, at several 

 localities within the Arctic Circle, also in many 

 other regions of both the Old and the New World. 

 These records afford an exceptionally striking 

 illustration of the possibilities offered by a study 

 of the herbaria of the rocks of connecting the 

 present with the past, of following the wanderings 

 over the world and of tracing the rise and fall in 



