. III. DIST. CHAR. Soil. 169 



B. 152. THE SEAT (Sedes) is that part of the 

 soil in which the reliqtiium and its matrix, if dis- 

 tinct,, are lodged when no distinct or separate ma- 

 trix immediately surrounds the extraneous body, 

 the seat is properly considered to be the matrix in- 

 definitely extended (matrix continuata). 



The seat is either aqueous or mineral. 



a. 153. AQUEOUS SEATS (Secies aquarice) are 

 Jakes, running waters., &c. in which reliqui a ( fre- 

 quently petrifactions of wood f ) occasionally occur. 



f- It has been a subject of dispute, whether the siliceous petri- 

 factions of wood found in water, have been generated there, or in 

 the surrounding and subjacent strata Some authors supposing, 

 that extraneous bodies thus circumstanced may have been detached 

 by the agency of torrents, floods, &c. from their original beds, and 

 subsequently reposited in their present situation. When the con- 

 tiguous mineral bodies are such, as are known to contain petrified 

 wood that is, when they consist of sand, gravel, clay, &c. forming 

 alluvial beds, or masses lodged in the veins or fissures of more an- 

 cient strata this may undoubtedly have been the case : but, as the 

 petrifaction of the wood thus imbedded must have been effected 

 by the percolation of water impregnated with siliceous matter, we 

 see no reason to deny the possibility of the same eflect being pro- 

 duced by the waters of lakes and rivers, when they contain (as 

 some undoubtedly do) siliceous earth, either in a dissolved or sus- 

 pended state. Indeed, the petrifying quality of several waters, in 

 various parts of the world, seems now to be pretty generally ac- 

 knowledged that of the water of Lough Neagh, in Ireland, was 

 particularly eminent at one time a*id the water-courses of our 

 mines in Derbyshire have, within our own knowledge, produced 

 some very fine specimens of woodstone. Many of the lakes in 



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