as compared with that of the present day. 367 



some of them purely botanical, whilst others are more general, and 

 refer to the dependence of vegetation upon the condition of the area 

 it covers. 



Some acquaintance with systematic botany is the first requisite : 

 through this alone can any approximation to the living affinities of 

 the fossil be obtained. It should embrace not only a knowledge of 

 the principal groupes or natural order under which all plants are ar- 

 ranged, but a familiarity with vegetable anatomy ; for when the 

 stem or trunk alone is preserved, which is often the case, a minute 

 examination of its tissues is the sole method of determining its posi- 

 tion in the natural series. 



A solution of the difficulties which this special knowledge will 

 tend to remove is of the highest interest to botanists, though com- 

 paratively preliminary to the object of the geologist, whose inquiry 

 is, what were the general features of such a vegetation as has affected 

 the formation of a seam of coal, both as regards quantity and kind ; 

 as regards quantity, inasmuch as the growth was either wonderfully 

 rapid or more tardy, but prolonged under uniform conditions ; and, 

 as regards kind, from certain species, genera, or orders, being parti- 

 cularly adapted by their quick growth, their gregarious habits, and 

 their continued appropriation of certain areas to produce those vast 

 accumulations, the explanation of whose origin is still an unsolved 

 problem. Other questions, which a study of living plants alone can 

 answer, refer to the sorts of plants best calculated to thrive in such 

 a uniform soil as the underclay upon which each bed of coal rests, 

 and into which some of the vegetables have certainly been rooted. 

 What form of surface is best fitted to retain so mobile a mass of 

 debris as the coal was previous to its compression and hardening ? 

 What degree of dryness would be most favourable to such an accu- 

 mulation, consistently with an energetic growth of vegetation \ 



The above considerations presuppose some general ideas of the ve- 

 getations both of the tropics and cooler latitudes, of mountain-chains, 

 table-lands, valleys, and estuaries ; moi'e especially of countries cha- 

 racterised by equable or by excessive or extreme climates, as com- 

 pared with continents, and of humid and desert districts ; in short, 

 of all the complex associations with, or dependence of botanical cha- 

 racter upon, surface, soil, and climate, which the globe presents. 



The want of this kind of information amongst many naturalists, 

 and the neglect of its application by others, have caused those utterly 

 contradictory opinions which have been expressed regarding the ori- 

 gin of coal,* and unnecessarily complicated the subject. The botanist 



* The looseness of the speculations hitherto advanced on the relationship of 

 the coal flora to such physical conditions as climate, cannot be better illustrated 

 than by the fact that the Sigillarise (wliich have undoubtedly contributed 

 largely to the formation of coal) are considered by some naturalists to be allied 



