INTRODUCTION. 27 



of sulphates. Moreover, there can be no doubt that cinnabar, lead-glance, 

 barytes, and sulphur are found merely filling fissures in wood that is in- 

 crusted and turned into coal. Brown ironstone fossils ought as a rule to 

 originate in the oxidation of the pyrites, those in red ironstone in the 

 decomposition of the carbonate of iron which was the original petrifying 

 agent. Lastly, Goppert 1 obtained petrifactions in oxide of iron and metallic 

 silver by artificial means. These experiments resulted, according to his 

 own account, in the filling of the cells with the precipitates, though im- 

 perfectly and with a small amount only of their substance. The skeletons 

 in silver of parts of plants (Erica mediterranea), which had lain a year in 

 concentrated solution of silver, were obtained in their natural form by 

 subjecting them to strong heat; gold chloride and platinum chloride are 

 said to have given similar results. The less solid skeletons in oxide of 

 iron were produced in the same way after soaking in sulphate of iron. 



Even true petrifaction appears to be often preceded by a complete 

 or partial filling of the lumina of the cells. The carbonates of the alkaline 

 earths, for example, which, as has been before observed, are the most perfect 

 soluble agents of petrifaction, also occur, but more rarely, as substances 

 merely filling the cells, and after destruction of the organic matters they 

 may be isolated in the form of spiculae representing the several elements. 

 I 2 have observed this condition in a piece of wood from the Upper Permian 

 beds of Frankenberg, which contained so much coal that the sections 

 proved to be entirely opaque ; no view of the substance could be obtained 

 till the coal had been removed in the flame of the blowpipe, and the 

 cell-spiculae converted into potash had been isolated. Goppert 3 observed 

 the commencement of the process of calcification in an apparently ana- 

 logous manner in recent wood. He obtained some beech-wood from 

 a Roman conduit at Eilsen in the district of Biickeburg, in the interior of 

 which were irregular points of calcification, and these would no doubt have 

 united if the process had been continued. The same wood has been more 

 closely examined and figured by Stokes 4 . Similar phenomena were 

 observed in the wood of an oak-tree found in a brook at Gera by Herr 

 Laspe; when it was polished, its cells and vessels proved to be entirely 

 filled with carbonate of lime. Another similar case is described by 

 Daubree 5 , in which groups of points of calcification were found inside the 

 wooden piles of a Roman canal at Bourbonne les Bains. 



The same forms of petrifaction may also be distinguished in the case 

 of silicification. Here too the more frequent case is the dissemination of 

 the silica throughout the organic remains, while internal cavities in them 

 are very often wholly or partially preserved and form glands lined with 



1 Goppert (17). 2 Solms-Laubach, Graf zu (1). 3 Goppert (1) and (17). * Stokes (1). 

 Daubree (1). 



