DISTRIBUTION IN TIME AND SPACE. 63 



lerns formed a far smaller part of the vegetation of these later 

 ages than in the preceding Carboniferous, and even approxi- 

 mated to that of the present. Six Cretaceous and twenty-four 

 Tertiary species have been catalogued,* including species in 

 the existing genera Lygodium, Pterts, Woodivardia,Dryopteris, 

 Gymnogramme, etc., as well as some related to genera abundant 

 in earlier formations. No living species is found fossil, unless 

 Dr. Newberry's variety of Onoclea sensibilis becomes estab- 

 lished.t In the course of geologic history, however, we can 

 trace a gradual approximation to the modern types from the 

 generalized forms of Devonian and Carboniferous times. 



144. Fern Allies. Ophioglossum dates back to the Ter- 

 tiary period with one species. The order EQUISETACE^E have 

 existed since the coal period and the genus Equisetitm since the 

 Triassic. The order CALAMARIACE/E, which combined charac- 

 ters of modern Equiseta and Conifers, came into existence in the 

 Devonian, but became extinct before the close of the Permian. 

 Illustrations of Calamites can be seen at the left-hand corner of 

 the frontispiece, also under the tree-fern in the centre. The 

 club- mosses proper have been in existence since the Devonian, 

 and the genus Lycopodium since the Carboniferous. Selaginella 

 has never been found fossil, but its near relatives belonging to 

 the extinct orders LEPIDODENDRACE^E and SIGILLARIACE.E 

 were very abundant in the Palaeozoic era, particularly during 

 the Carboniferous, where they formed the largest part of the 

 forest vegetation, reaching in some instances a height of sev- 

 enty to one hundred feet. The former possessed characters 

 connecting modern club-mosses with Conifers, while the latter 



* Tenth report, Hayden Geological Survey of the Territories. Washing- 

 ton, 1878. 



t Prof. Lesquereux writes me: "Though analogous by the nervation, I 

 doubt the identity on account of the coriaceous character of that fossil fern, 

 which I have not seen in any variety of O. sensibilis now living. " Principal 

 Da wson, however, writes : "The Onoclea sensibilis of the Laramie is truly 

 that species, and I have found with it in our Manitoba formations another 

 modern fern, Davallia tenuifolia." 



