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piece of living alche-ny, the blade of grass, which weaves its expanding form 

 and crystallises in cells of sunshine, water, carbonic acid, and ammonia ; — and 

 tbat material which was vivified and utilised in those extinct organisms may 

 serve in endless metamorphoses, for we know not what organisms yet to come. 

 AVhat a testimony again to the uniformity and permanence of nature's laws is 

 that living link the Isoetcs, found in a pool near Darnford ; but for the exist- 

 ence of that small water plant the large trees of the coal forests would present 

 in the growth of their stems (that remarkable zone of spherical cells which sur- 

 rounds their woody cylinder), an unexplained anomaly, but the rays of scien- 

 tific light extracted from the separate investigations of a Witham and Car- 

 ruthers here converge in the elucidation of these interesting types. 



Placed side by side, the fossil witness, the Lcpidostrobus, of the coal, and 

 the living Lycopodia of these hills, exhibit a close parallel in the size and 

 relative position of their microspores and microspores. This living link, the 

 Lycopodiam, carries us still further into the domains of the past, for in the Led- 

 bury shales and Upper Ludlow bone bed, twigs, branches, and spore cases, or 

 Pacytheca, give the first real proof of dry land. 



We thus derive from such a record that successive geological epochs 

 are in a measure equivalent to the various parallels of latitude marking 

 the zones and climates of the present surface of the earth ; for the Coniferse 

 of the carboniferous age, presenting as they do few of the concentric lines (the 

 marks of annual growth), are exactly met by the same peculiarity of structure 

 in the tropical trees of South America now, and we see how the Lepidodeadron 

 then, as the Lycopodlum so abundant on these hills is now, was so well adapted 

 to form part of the flora of that epoch in which vegetable mould was scarce, 

 and when the surface of the globe consisted chiefly of barren rocks and dismal 

 swamps. The more closely we study the numerical laws of plant distribution, 

 the ratio of certain families to the whole number of species, when and where 

 each family reaches its maximum number of species or its highest develop- 

 ment, the clearer we find that the replacement of one species by another in space 

 has its exact parallel in past time, so as to preserve a certain ratio of parti- 

 cular families to the whole mass of the Flora, testifying likewise to a certain 

 primitive plan of plant distribution. Further than this, the supposition of 

 specific centres from which diffusion has been effected by emigration and other 

 agencies, appears to be the natural outcome of all investigations in the his- 

 tory of any family of plants. 



For as the variations produced by a number or the force of external 

 agents, as already noticed, are strictly coincident with an extended range of 

 any gven family, and are such as to induce us to separate the extremes when 

 the intermediate forms are absent ; still, if we tr.ivel back, in time, guided 

 by the analogy of other organised forms, we lose one after another the 

 more specialised groups, and are able to follow out our converging lines cf 

 existence till they meet in the same point, and this remote. So again in 

 the animal world we find various tribes of any species originally, as it would 



