142 PEOCEEPINGS OP THE aEOIOGICAL SOCIETT. [DcC. 20, 



more moist and equable climate than that which now subsists; 

 so that we may suppose the growth of such plants to have been 

 more rapid than it is at present. These plants would thus lead us 

 to infer a warm and insular climate, perhaps influenced by that sup- 

 posed excess of carbonic acid in the atmosphere, which, as TyndaU 

 and Hunt inform us, would promote warmth and moistui^e by im- 

 peding terrestrial radiation. With this would also agree the fact 

 that the Conifers have woody tissues resembling those of the pine 

 trees of the milder climates of the southern hemisphere at present. 



If we apply these considerations to Sir/illaria, we may infer that 

 the conditions of moisture and uniformity of temperature favourable 

 to ferns and Lycajpodiacece were also favourable to these curious 

 plants. They must have been perennial ; and the resemblance of their 

 trunks to those of Cycads, together with their hard and narrow 

 leaves, would lead us to infer that their growth must have been very 

 slow. A similar inference may be drawn from the evidences of very 

 slow and regular expansion presented by the lower parts of their 

 stems. On the other haud^ the distance, of a foot or more, which 

 often intervenes between the transverse rows of scars, marking pro- 

 bably annual fructification, would indicate a more rapid rate of 

 growth. Further, it may be inferred, from the structui^e of their 

 roots and of their thick inner bark, that these, as in Cycads, were re- 

 ceptacles for great quantities of starch, and that the lives of these 

 plants presented alternations of starch-accumulation and of expen- 

 ditui'e of this in the production of leaves, wood, and abimdant inflo- 

 rescence. They would thus, perhaps for several years, grow veiy 

 slowly, and then put forth a great mass of fructification, after which 

 perhaps many of the individuals would die, or again remain for a long- 

 time in an inactive state. This view would, I think, very well har- 

 monize mth the structure of these plants, and also with the mode of 

 their entombment in the coal. 



Erom the manner of the association of Calamites with erect Sigil- 

 larice, I infer that the former were, of all the plants of the Coal-for- 

 mation, those of most rapid dissemination and growth. They appear 

 to have first taken possession of emerging banks of sand and mud, 

 to have promoted the accumulation of sediment on inimdated 

 areas, and to have protected the exposed margins of the forests of 

 Sic/illarice. 



In applying any conclusions as to the rate of growth of Carboni- 

 ferous plants to the accumulation of coal, we must take into account 

 the probable rate of decay of vegetable matter. When we consider 

 the probable wetness of the soils on which the plants which pro- 

 duced the coal grew, the density of the forests, and the possible 

 excess of carbonic acid in the atmosphere of these swamps, we must 

 be prepared to admit that, notwithstanding the warmth and humidity, 

 the conditions must have been favourable to the preservation of ve- 

 getable matter. Still the hollow cylinders of bark, the little frag- 

 ments of decayed wood in the form of mineral charcoal, and the 

 detached vascular bundles of ferns, testify to an enormous amount of 

 decay, and show that, however great the accumulation of coal, it 



