AS COMPARED WITH THAT OF THE PRESENT DAY. 415 



chiefly at the base of the frond-stem or stipes, a part of the plant inva- 

 riably wanting in the fossil. Smaller scales, hairs, and glands are most 

 frequently confined to the under surface of the frond, which, from 

 various causes, and this amongst others, is almost invariably the one 

 that is united to the rock in petrified ferns, and therefore unavailable 

 for botanical examination. 



Sigillaria. 



Perhaps the most important plant in the coal formation, forming a 

 conspicuous feature in almost every field, appearing in all the strata, and 

 distributed from Spain to Scotland and from Virginia to Newfoundland 

 in America. Upwards of GO species have been described ; with how little 

 precision may be inferred from the fact mentioned above, that many of 

 them have been proved mere varieties, in a solitary case even four 

 being reduceable to one.* Under the names of '* bottoms" and " bell- 

 moulds " the stumps of Sigillaria are well known to the colliers, as dan- 

 gerous associates of the shale roofs in the workings, immediately above 

 the coal. They are generally but a few feet high, though sometimes two 

 yards broad at their expanded bases, they are truncated at the top, and 

 retain their position in the shales after the removal of the coal upon 

 which they rested, being supported by the pressure of the atmosphere 

 and the cohesion of their smooth sides. Unless propped, they, after 

 a time, lose their hold and fall in, sometimes severely injuring the 

 workmen. So common are they, that I have in many South Wales and 

 other collieries counted five or six in the space of a few fathoms, always 

 suggesting the idea of the erect stumps of trees in a forest. 



In the shales surrounding the bases of these stumps are found pros- 

 trate stems, bearing markings similar to what sometimes appear on the 

 stumps. It is, however, generally the case that the markings of the 

 stumps are very obscure or wholly obliterated, as usually occurs on the 

 lower parts of the stems of those plants which at an earlier stage bear 

 deciduous organs. This absence of marking has been urged in proof 

 of these stumps not being Sigillaria? at all ; but we know no other 

 genus to which they can be referred ; and in the noble erect specimens 

 discovered and examined by Mr. Binney, the gradual evanescence of the 

 scars or even flutings of the trunk at a few feet above the root, is very 

 decidedly shown in most instances, though in some they may be traced 

 almost to the base. 



That the Sigillaria? were of a very brittle and probably lax tissue, is 

 I think evident by the constantly truncated upper end of the stumps 

 in the shales, their never being prostrated entire, and the singular com- 



* Mr. Binney, of Manchester, showed me a Sigillaria, in which the characters of 

 S. catenulata, reniformis, organum, and alternans were all displayed, a fact he has alluded 

 to in the Manchester Philosophical Magazine for October, 1844. 



