4 INTRODUCTION. 



and of chalcedony. It is the one of all others which ensures the most per- 

 fect preservation of the enclosed remains. Silicified woods are found in 

 extraordinary quantity in all formations ; it is more rare to find the more 

 delicate parts of plants, leaves, seeds, or the fructifications of ferns well 

 preserved in the silicified state. Specimens of the latter kind occur 

 chiefly in the hornstones of the Rothliegende at Chemnitz and in the 

 Plauensche Grund near Dresden, in the same formation at Autun, and in the 

 siliceous fragments of Grand' Croix near St. Etienne, which represent a 

 fossil forest. These pebbles, which belong to the uppermost beds of the 

 Carboniferous and supplied Renault with the principal material for his 

 admirable researches, will be discussed again at greater length in a 

 succeeding page. 



The next in order of importance are the isomorphous carbonates of 

 calcium, magnesium, and iron, CA CO^, CA CO 3 + Mg CO 3 , Fe CO 3 . Gop- 

 pert is of opinion that calcium carbonate is present in some petrifactions in 

 the form of arragonite ; it occurs in most cases as calc-spar. Here too the 

 remains of plants may in certain circumstances be in an excellent state of 

 preservation. This kind of petrifaction is found in great abundance in the 

 Coal-measures of England and of the district of the Ruhr. It occurs also in 

 North America in the State of Missouri, but the remains, so far as I know, are 

 still undescribed. I have seen two fragments in F. Romer's collection, but 

 unfortunately the place where they were found is not distinctly stated- 

 Their surface resembles that of the Stigmarias, and transverse sections 

 show that they contain a confused mass of fragments of Stigmarias and 

 of leaf-stalks of Ferns in different states of preservation. Petrifactions 

 in carbonate of iron very commonly form the nucleus of clay iron-stone 

 nodules. 



Wood petrified in fluor-spar is very rarely found, but it occurs occa- 

 sionally in the Rothliegende of the Erzgebirge, and is particularly 

 mentioned by Knop 1 and Sterzel 2 . Petrifaction in gypsum is still more 

 rare ; the only instance of it which I have been able to find in the 

 literature is that of the stem of a Conifer, which Gb'ppert 3 obtained from 

 the gypsum-quarries of Katscher in Silesia, and has described under the 

 name of Pinites gypsaceus. It is moreover doubtful whether the speci- 

 men is truly petrified, since it shows a brownish colour in places and is 

 extremely rich in bituminous substances. Calcium triphosphate is also 

 known as a petrifying agent ; roundish lumps of this material containing 

 well-preserved and determinable woods are found, according to Vater 4 , in 

 abundance in beds of phosphorite in Brunswick. Portions of the wood of 

 Calamites preserved in this phosphate, according to Stur 5 , are found also in 



Knop (I). " Sterzel (2). 3 Goppert (r. Vater (1). Stnr (8), p. 418. 



