430 ON A SUBMARINE FOREST IN THE FRITH OF TAY. 



3. Several changes of a chemical kind have already taken 

 place in this stratum of peat. The fibrous structure of much 

 of the vegetable matter is obliterated, small portions of the 

 reeds, and even of the wood, are so changed as to resemble 

 wood-coal ; — changes these, which plainly intimate, that a 

 process is going on, by which, in time, that which is now peat 

 may become coal. In the crevices of some portions of the 

 wood I have detected thin crusts of the blue phosphat of iron. 

 It is rather singular to have found some of the roots in the 

 soft clay changed into iron-pyrites. This change has chiefly 

 taken place in the bark, and in such cases the wood and pith 

 are wanting. In one example, however, the pith remained, 

 and had likewise been converted into pyrites. In many cases 

 the clay is full of tubular cavities, the remains of the spaces 

 which the roots or stems of plants once occupied. The walls 

 of these cavities are usually of a darker colour, and firmer tex- 

 ture, than the surrounding matter, and have evidently under- 

 gone some change, in consequence of the decomposition of 

 the vegetable matter. In some cases, the epidermis of the 

 plant remains in contact with the surrounding clay, while 

 the matter of the interior has disappeared. Into these cavi- 

 ties the clayey matter enters slowly, and fills the mould which 

 the decomposition of the plant has prepared. This may be 

 regarded as a process similar to the one which has taken place 

 in those vegetable petrifactions so common in the argillace- 

 ous and arenaceous beds of the coal-formation, in which slate- 

 clay, clay-ironstone and sandstone, are exhibited under the 

 external forms of plants. 



Should these observations appear interesting or satisfactory, 

 I shall feel disposed to transmit, at no distant period, the re- 

 sult 



