the Process of Petrifaction. 77 



a distance from their original locality, and the term ought always 

 to be so limited. At an early period it was attempted to explain 

 the phenomenon. Agricola* thought that it took place by means 

 of a liquid containing stony matter, which penetrated the spaces 

 of vegetable and animal bodies, and gradually communicated to 

 them a stony character. The later mineralogists, as Scheuchzer, 

 Walch, Schulze, Schroter, Wallerius the elder, agreed in the 

 opinion, that, when a body is petrified, or converted into metal, 

 an exhalation must first proceed from it by which it loses cer- 

 tain particles, in whose room earthy or metallic ones enter, and 

 that thus at last the body is converted into stone or metal. The 

 means by which the exhalation is promoted in animals is, accord- 

 ing to the same view, calcination, and in plants the reduction to 

 earth. More recently, so far as is known to me, no one has at- 

 tempted to trace out this process by an experimental inquiry, 

 it being probably supposed that too long a time would be re- 

 required for obtaining the desired result. In a lecture f deli- 

 vered in London by Faraday, at the beginning of 1836, he says, 

 " that we have no knowledge whatsoever of the nature of this 

 process, for the instances of recent fossilization, which have as 

 yet been produced from various places, are mere incrustations 

 of calcareous or even of siliceous matter, where there has been 

 no preservation of organic forms, — none of that beautiful and 

 incomprehensible substitution which, while it excites our admi- 

 ration, baffles our curiosity." For a long time I was occupied 

 in examining the way which nature had employed in this pro- 

 cess. First of all, I made the experiment with iron. I intro- 

 duced plants into a moderately concentrated solution of sulphate 

 of iron, and left them there until the separation of the salt on the 

 outer portions of the plants shewed the sufficient saturation ; or 

 I at once soaked smaller portions of plants and sections of wood 

 in the same solution for several days. They were then dried 

 and heated till they no longer suffered alteration of volume, or 

 imtil every trace of organic matter had disappeared. On cool- 

 ing them I found the oxide thus produced in the Jurm of the 

 plant. I now took thin vertical sections of the Pinus sylvestris, 

 treated them in the same manner, and found them so well pre- 



* Lib. 3, de ortu ct causis subterran. p. 007 > Lib. 7> de nalura /osailium, p. 639. 

 t The Lancet, February 6. 1836. 



