172 



HISTORICAL GEOLOGY 



Filices (true Ferns) were very abundant and diversified, both 

 as tree-like forms and as small, herbaceous forms. Both forms 

 were very similar in appearance to those now living in tropical 

 and temperate climates (Figs. 99-100). 



Cycadofilices ("Seed-ferns"), which were common in the Penn- 

 sylvanian, comprise a remarkable group of plants recently regarded 

 as transitional between the Cryptogams and Phanerogams. They 

 possessed seeds but not flowers and showed many features which 

 seem to make them the connecting link between the Filices and the 



Cycads, hence the name "Cycadofili- 

 ces." The seeds were arranged on 

 the leaves. There is considerable dif- 

 ference of opinion concerning the 

 relations and affinities of this remark- 

 able group of plants, now long extinct 

 (Fig. 102). 



Gymnosperms. — Of these the most 

 abundant representatives were the 

 Cordaites. They were comparatively 

 slender trees which attained a diam- 

 eter of 2 or 3 feet and a height of 90 

 feet or more (see Fig. 103). The 

 branches, which were given off only 

 toward the top of the trunk, were 

 supplied with numerous, long, very 

 simple, parallel- veined, strap-shaped 

 leaves notable for great size, some- 

 times 5 or 6 feet long and 5 or 6 inches wide. The trunks were 

 covered with thick bark, while inside there was much pith. Many 

 specimens have been well preserved. They were important contrib- 

 utors to the formation of some coal beds. Thej^ possessed certain 

 features or structures of the Seed-ferns, Conifers, C3^cads, and Gink- 

 gos in addition to their own characteristics. Cordaites thus afford 

 a fine illustration of a generalized tj^pe of plant, that is to say one 

 which combined the characters of several distinct (some later) forms. 

 True Cycads and Conifers are not certainly known to have 

 existed in the Pennsylvanian period, though some paleobotanists 

 claim their existence. 



Protozoans. — Foraminifers were very abundant as proved by 

 the vast numbers of tiny wheat-like shells which contributed much 



Fig. 100 

 A Living Tree-fern. (From 

 Le Conte's "Geology," per- 

 mission of D. Appleton and 

 Company.) 



