198 SXJPPLEMENTAEY NOTES. 



a material in the constitution of fossil wood and shells, as well as in pseudo-morphic crystals,' 

 consists in the ready solution of silex in water at a high temperature (a fact affirmed by 

 Bergman^ under great pressure, whenever an alkali is present, as is seen at the present time 

 in many volcanic regions, and its ready deposition again when the water cools. A mere 

 heated aqueous solution of silica, under a high pressure, is sufficient to explain the phenomenon 

 of the silicification of organic structures. Mr. Dana states that "a crystal of calc-spar in 

 such a fluid, being exposed to solution from the action of the heated water alone, the silica 

 deposits itself gradually on a reduction of temperature, and takes the place of the lime, atom by 

 atom, as soon as set free. Every siliclfied fossil is an example of this pseudo-morphism ; 

 but there seems to be no union of the silica with the lime, for silicate of lime is of rare 

 occurrence.^ 



XX. Stigmaria, Sigillaria, Sj-g. — The most remarkable peculiarity of the flora of the carboni- 

 ferous period is the immense numerical preponderance of the vascular or higher tribes of crypto- 

 gamic plants, which amount to two-thirds of the species described. With these are associated a 

 few Palms, Conifera, Cycadeae, and dicotyledonous plants, allied to the Cactea and Euphorbiacea. 

 The number and magnitude of the vegetables bearing an analogy to the Ductulosce, but difiering 

 from existino- species and genera, constitute therefore the most important botanical feature of 

 the carboniferous flora. Thus we have plants allied to the Equisetum, or mare's-tail (Calamites), 

 eighteen inches in circumference, and from thirty to forty feet high ; Zamia-like coniferse 

 {SigiUariw) fifty feet high ; and arborescent club-mosses {Lepidodendra) attaining an altitude 

 of sixty or seventy feet. Of this ancient flora, the fossil plants whose stems have been named 

 Sigillaria (see Plate XXI.), and their roots Stigmaria, are especially remarkable in consequence 

 of the peculiar circumstances under which upright examples of these trees are occasionally 

 met with. Referring for details to "Wonders of Geology," Lecture VII., I purpose describing 

 in this place the facts recently brought to light, which prove that certain species of Stigmaria 

 are the roots of SigillariEe ; while others in all probability belong to Lepidodendra : — an opinion 

 maintained more than thirty years ago by the Kev. H. Steinhauer.* To the late Mr. Binney 

 we are indebted for the first confirmation of the inference of my friend, M. Adolphe Brongniart, 

 (derived from an examination of the structure of those bodies,) that the Stigmarise are the veritable 

 roots of Sigillarise. At St. Helen's, near Liverpool, Mr. Binney discovered, in 1844, an upright 

 trunk of a Sigillaria, nine feet high, to which were attached ten roots, several feet long, 

 that extended into the under clay in their natural position -^ and these roots were un- 

 questionable Stigmaria, the tubercles with their attached rootlets being clearly displayed. 

 In the floor of the Victoria Mine at Dunkinfold, near Manchester, at the depth of 1,100 feet 

 from the surface, Mr. Binney also discovered a magnificent specimen of Sigillaria, which 

 exhibited on its stem the respective chai-acters of three supposed species, and had stigmaria- 

 roots extending twenty feet. 



In the Sydney coal-field at Cape Breton, Mr. Eichard Brown has observed several upright 



' Pseudo-morphic crystals are crystals moulded in the cavities left by other crystals, which they hare replaced. See Dr. 

 Blum on pseudo-morphous minerals ; and Mr. Jefferey's experiments on the solution of silica in heated vapour ; Wonders of 

 Geology, p. 100. 



2 Bergman first determined the solubility of silex in simple water, aided by heat, and demonstrated its existence in the 

 Geysers, and other boiling springs of Iceland. Parkinson, Org. Rem., vol. i. p. 324. 



^ See my "Notes on a microscopical examination of chalk and flint," Annals of Natural Histoiy, August 1845. 



* Transactions of the American Philosophical Society, N"ew Series, vol. i. 



^ See Medals of Creation, vol. i. p. 143, 



