594 



GEOLOGY. 



boniferous times they had more comprehensive characters, and were 

 in part more primitive than now, and in part more advanced, or at 

 least more closely allied to the higher type, gymnosperms. The fruiting 

 organs, however, were only rarely well preserved, and this limits a 



Fig. 277. — A group of plant fossils, occurring in concretions in the Coal Measures at 

 Mazon Creek, 111. : a, Neuropteris decipiens Lx. ; b, and c, Pecopteris unita Brgt.; 

 d, Callipteridium sp.; e, Annularia longifolia Brgt.; /, Annularia spenophylloides 

 Zenk., g, Cordianthus sp., and h, Lepidostrobus sp. 



precise knowledge of rank and kinship in many species. The majority 

 were herbaceous, but there were many tree fern some of which reached 

 heights of sixty feet. One of these is represented in the right rear cen- 

 ter of the group in Fig. 275. The fronds of several prominent genera 

 are illustrated in Fig. 276, some of which, however, probably belonged 

 to. transitional types, and not true ferns. The ferns seem to have been 



