184 APPENDIX. 



of which so many portions remain ; but I thought I recognized some which are now growing in 

 the neighboring marshes, such as flags, cattails, &c. I hope, however, that you, or some of your 

 scientific friends, will visit the place, and obtain more accurate information than I am competent 

 to give." 



F. — Page 152. 



The following letter to the author presents the views of the distinguished Professor Silliman 

 on the subject of Petrifaction: — 



" In reply to your letter, I can very briefly state my views regarding petrifaction. It appears 

 to me to arise from a gradual substitution of inorganic for organic matter, the tissues of the 

 latter serving as moulds in which the former is cast by gradual percolation or infiltration ; and 

 it becomes firm by cohesion. 



" Petrifactions being chiefly siliceous or calcareous or ferruginous, and all these matters 

 being contained in natural waters, may therefore be introduced through their agency. 



" It is very possible that the immense petrified forests — the siliceous, I mean — may have 

 been lapidified by hot or tepid volcanic waters, holding silicates of alkalies in solution. The 

 sites of such forests may, by subsidence, have been lowered down beneath the waves ; and hot 

 waters, charged with silicates, may have continued to flow from a focal point beneath, and thus 

 the trees may have become stone. The geysers of Iceland and the hot silicated fountains of the 

 Azores produce changes upon organic bodies analogous to petrifaction. Submersion by sub- 

 sidence has been so frequent a geological phenomenon, that it is easy to extend this view to 

 calcareous and ferruginous petrifactions, which may be produced in the same manner with or 

 without the aid of heat. The soft parts of organic, and especially of animal bodies, are rarely 

 petrified, and in general only the firm fabric, such as bones, crusts, and woody fibre, which 

 appear to be sufficiently persistent to endure for the requisite period of time. Shells, being 

 already chiefly mineral matter, are more rarely changed, except by a substitution of inorganic 

 matter for the gelatine, or other animal matter, which they contain. Still, instances are not very 

 uncommon of silicified shells, silicified sponges and corals, &c. ; and siliceous and calcareous 

 casts frequently occupy the interior of shells, thus copying both their form, and that of the 

 included animal. 



" I have a portion of a dicotyledonous tree, obtained in a railway cut near Baltimore, which 

 is perfect haematite ; and still the fibre is as distinct as it was in the living tree. 



