DESCRIPTION OF TUE SPECIES. 229 



of preservation. The leaves on the upper surface, after the settling of the 

 twig on the bottom, were most exposed to the action of the water and were 

 removed, while those that were attached to the under surfiice, being held 

 in place by the pressure of the superincumbent stem, were retained. Most 

 of the leaves that appear to be attached to the sides of the stems no doubt 

 are really attached to their under surface. This seems to be the case in 

 PI. CI, Fig. 2, and PI. CII, Fig. 3. The ends of the large stems in these 

 figures are broken off. It is, then, most probable that the leaves were scat- 

 tered spirally around the larger stems. The leaves seem to have been 

 attached by their entire unnarrowed bases and to have been directed 

 upwards towards the summits of the stems. Hence we find them some- 

 times curved at base as Heer^ has depicted, but I have seen none so much 

 bent or so regularly, as those of Heer. 



The nerves are very obscure, and the leaves, even the best preserved, 

 rarely show any traces of them, for they seem to have been slender and 

 immersed in the leaf-substance. Generally only fine stria? are visible on 

 them, even with the help of a lens. They seem to be about four in number 

 and parallel. No difference in strength was noted, as Heer intimated. The 

 length of some of the leaves must have been very considerable, for some 

 fragments, with both the base and summit missing, were as much as IS*"" 

 long. In PI. cm. Figs. G, 8, 9, are given some fragments of leaves from 

 the 72d mile-post near Brooke, where detached leaves occur on some por- 

 tions of the shale in considerable numbers, crowded together or overlying 

 one another. In some cases, as in 8* and 6*, they show four very fine 

 nerves. In others, as G'', no nerves are seen, but the leaves appear smootli 

 and convex from pressure. Again, in some cases, us in (i", only one nerve 

 is visible. Sometimes, as in G'' and G'', the nerves vary in strengtli and are 

 vaguely shown. These differences are no doubt due to the accidents of 

 preservation. Sometimes it seems that apparent nerves are longitudinal 

 wrinkles or folds in the leaves caused by pressure. Tliis seems to be the 

 case in G* and G*. 



On the hill-side near Potomac Run a good many detached fragments 

 of long and very narrow leaves with four very fine nerves occur scattered 



' Flor. Foss. Arctic.!, vol. 6, jit. I, PI. VII, Figs. lO-l".'. 



