70 AN INTRODUCTION TO THE STUDY OF FOSSILS 



world, though it may possibly be native to western China. It 

 is the last member of a race that is seen by the fossil records to 

 have spread over all the world. This race, the Ginkgoales, 

 was especially numerous and widespread in the Jurassic and was 

 still abundant in Cretaceous time. Leaves and flowers of 

 representatives of this order are found in rocks of these ages 

 in Europe, northern Siberia, Greenland, Spitzbergen, China, 

 Turkestan, Australia, South Africa and the Pacific Coast of 

 America. In at least the earlier part of the Tertiary, the ginkgo 

 flourished in Alaska, Greenland, and the northern part of Great 

 Britain. Because of its great antiquity and isolated position 

 it has been called a " living fossil." It is supposed to have 

 arisen from the group of the Cordaitales. 



1. Describe the ginkgo tree. What is its common name and 

 from what derived ? 



2. What is the geologic range of this order ? 



3. Discuss the present and former geographic distribution of 

 the ginkgo tree. Can you account for this difference ? 



Order E, Coniferales 



This order includes the conspicuous gymnosperm vegetation 

 of the north temperate regions, made up of trees and shrubs, 

 mostly evergreen, usually with rigid, needle- or scale-like leaves 

 and wdth male and female cones. The conifers were probably 

 derived from the Cordaitales of the Paleozoic, retaining fewer 

 primitive characters than the Ginkgoales, but derived from the 

 same source. Living conifers are represented by forty genera 

 and three hundred and fifty species. They are divided into 

 two families : 



(i) Taxacece, the yews. — With fleshy seeds and exposed 

 ovules. Comparatively modern, with no record below the 

 Comanchean, they already during this period formed an im- 

 portant element in the Potomac flora of eastern North 

 America. 



