1824.] Submarine Forest in the Frith of Tay. 297 



condition as to admit of the mechanical effects of subsidence 

 taking place. 



2. In the examination of the vegetable remains in this bed 

 of peat, and of others which have been investigated, I have 

 been led to conclude (contrary to the commonly received opi- 

 nion * ), that many of the supposed stems of reeds which occur 

 in a petrified state, are in tact roots. These roots, or rather 

 subterranean stems, such as the Arundo colorata and ph rag- 

 mites, Menyanthes trifoliata, and many other marsh plants 

 exhibit, frequently occur in beds of peat, in a dead state, and 

 exhibit their peculiar characters, when but few traces of the 

 stems to which they belonged can be detected. 



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 be- 

 come coal. In the crevices of some portions of the wood I 

 have detected thin crusts of the blue phosphate 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 texture, than the sur- 

 rounding matter, and have evidently undergone 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 cavities 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 petrifac- 

 tions so common in the argillaceous and arenaceous beds 

 of the coal-formation, in which slate-clay, clay-ironstone and 

 sandstone, are exhibited under the external forms of plants. 



* See Parkinson's Organic Remains, vol. i. p. 455. 



