FOSSIL PLANTS. 



663 



lities, but the plant is comparatively rare. Tliis 

 ibssil is a mould of fine grained sandstone, and 



236. 



F.ivulsiria Tesselata. 



■was about three feet long. It retains, on one 

 side, some of the carbonized vegetable substance 

 which also fills the cavities of many of the scars; 

 it is clearly and beautifully detached from the 

 enveloping sandstone on three sides, and some- 

 what flattened, so that a transverse section would 

 be an oval. The rows of scars run longitudin- 

 ally or parallel with the axis of the stem, with 

 perfect regularity, each row being separated by 

 a groove ; the rows are narrower and more strong- 

 ly marked on the side, which, from its shape, 

 would appear to have been subjected to the least 

 pressure. The scars in the middle of the area 

 are somewhat club-shaped, the central lobe much 

 elongated, and very various in width, and not so 

 deeply sunk as the shorter lateral ones. There 

 is no indication of a central woody axis ; and it 

 appears to have been the stem of some plant, the 

 leaves of which were placed so close together, 

 that their bases, which were square, were in con- 

 tact. It was probably dicotyledonous, and per- 

 haps allied to sigillaria. , 



Ferns. There are numerous species of ferns 

 found in the carboniferous strata, most com- 

 monly in the shale forming the roofs of the coal 

 seams ; but also frequently in the sandstone and 

 fresh water limestone underlying the sandstone. 

 These ferns are often beautifully preserved, yet 

 as in the recent species, it is often difficult to 

 an-ange and classify them. Like the other vege- 

 table fossils of the lower strata, they differ consi- 

 derably from recent genera and species, to which 

 they are naturally allied. 



In the known numbers of existing plants, ferns 

 bear a very considerable proportion. Thus we 

 have about 1500 known ferns, and 45,000 phan- 

 erogamic plants, being in the proportion of 1 to 

 30. In Europe, this proportion varies from 1'35, 

 to 1'80. In the tropics, the numbers are 1"36, 

 and 1-20. The circumstances most favourable 

 to the growth of these plants are humidity, 

 heat, and shade, and thus they find favourable 

 habitats in small wooded tropical islands, where 

 the surrounding ocean affords a constant supply 

 of moisture. 



In the coal strata, ferns greatly predominate 

 over all other vegetables. The present ascer- 

 tained number is about 120 species, forming 

 nearly a half of the fossil flora. These species 

 for the most part belong to the tribe of polypo- 

 diacese. In the table already given, we haVe 

 inserted the genera, and the following figures 

 will give a sufficient idea of a few of the species. 



237. 





Wimp 



Pecopteris Sphenoptpris 



lieterophyllum. dilatata. 



In general, these ferns are most beautifully pre- 

 served in the shale, and especially in some kinds 

 of fresh water limestone, as that of Burdiehousc, 

 near Edinburgh. In the bituminous shale at 

 Wardie, near Edinburgh, some specimens of the 

 splienoteris afflnis are so perfectly preserved, as to 

 admit of portions of the plant being taken up 

 entire, and pasted on paper like a recent fern. 

 Several fragments of the larger stems of arbor- 

 escent ferns are occasionally met with in the coal 

 strata. 



Lycopodites Williamsonis, (see cut 238, fig. a.) 

 This fossil plant is very common in the oolite of 

 Scarborough. It appears to have been a creeping 

 plant, like the recent It/copodium clavatum. The 

 stem is frequently branched, and concealed by the 

 base of the leaves, which are sessile, and of an 

 acute filiform shape ; one or two strongly marked 

 ridges run up the centre of each leaf, which ap- 

 pear to be the edges of angles. The leaves are 

 opposite, with frequently smaller ones interme- 

 diate. The surface of the stem is covered with 

 scales, apparently the base of leaves which have 

 lost their points. The stems are terminated by 

 a large oval head or cone, which is covered with 

 small hook-like processes, similar in form to the 

 leaflets, but smaller. When the bituminous 



