§ 31. ARTIFICIAL VEGETABLE PETRIFACTIONS. 709 



that the process began at an early period, and continued till 

 the whole vegetable structure was transmuted into stone." 



My lamented friend, the late Dr. Turner, in some admira- 

 ble comments on the subject of petrifaction, remarked, that 

 whenever the decomposition of an organic body has begun, 

 the elements into which it is resolved are in a condition 

 peculiarly favourable to their entering into new combina- 

 tions ; and that if water, charged with mineral matter, come 

 in contact with bodies in this state, a mutual action takes 

 place, new combinations result, and solid particles are pre- 

 cipitated, so as to occupy the place left vacant by the 

 decomposed organic substance. 



31. Artificial, Vegetable Petrifactions. — M. Gop- 

 pert has published the result of an interesting investigation 

 of the condition of fossil plants, and the process of petrifac- 

 tion. Layers of ironstone nodules, as we have previously 

 stated, are common in the carboniferous strata. They 

 appear to have once constituted continuous layers, the 

 nodules having been produced by segregation, i. e. the sub- 

 stance of which they are composed has separated from the 

 constituent parts of the rock after deposition.* The first 

 segregation often appears to have been caused by the 

 presence of some extraneous matter, sometimes a trilobite, 

 or a shell, and very commonly the leaf of a fern.f Mr. Par- 

 kinson had remarked, that the leaves in these nodules might 

 sometimes be separated in the form of a carbonaceous film; 

 and M. Goppert having found similar examples, was in- 

 duced to undertake a set of experiments. He placed fern- 

 leaves in clay, dried them in the shade, exposed them to a red 

 heat, and obtained striking resemblances to the fossil plants. 

 According to the degree of heat, the plant was found to be 

 either brown, shining black, or entirely lost, the impression 

 only remaining ; but in the latter case the surrounding clay 



* Sir H. De la Beche, Kesearches in Theoretical Geology, p. 96. 



f Medals of Creation, p. 81. 



3 a 2 



