INTRODUCTION. 5 



the uppermost beds of the Coal-measures. Grand' Eury 1 reports the presence 

 of similar fossils in the 'couche des Rochettes' and the 'couche des Littes/ 



Barytes, pyrites, red and brown iron-ore, argentiferous copper-glance, 

 and argillaceous earth are also said by various authors to be petrifying 

 agents 2 . How far the remains of plants preserved in these insoluble com- 

 pounds can really be regarded as true petrifactions must be considered in a 

 subsequent page. 



Lastly, amber must be mentioned as an organic medium of petrifaction 

 in so far as it incloses small pieces of coniferous wood perfectly resinised 

 and sunk in the amber, but with their substance still preserved, as we learn 

 from Berendt and Goppert 3 . Other organic inclosures in amber show a 

 different behaviour. 



While then true petrifactions are known by the fact that every part of 

 their substance is permeated by the petrifying material, incrusted remains 

 are on the contrary merely surrounded by the incrusting mass and inclosed 

 in it ; their substance is not otherwise affected, and may in process of time 

 be changed into coal, or, if the inclosing mass is of a porous nature, may 

 entirely decay and disappear. This has happened, for example, to all the 

 many insects and flowers which have been inclosed in amber. These 

 according to Conwentz 4 are represented by cavities, in which slight traces 

 of coal only are found. All the sculpturings on the outer surface of the 

 inclosed object are of course preserved on the wall of the cavity ; an im- 

 pression of the object is taken, whatever may become of its substance, and 

 this impression appears on the opposite faces of the cavity when it is broken 

 across. When the upper and under sides of the object differ in character, 

 as is the case with bifacial leaves, these differences appear on the two faces 

 as soon as any coal that may be present is removed. The finer the grain 

 of the inclosing mass, the more beautiful will be the impression, most beau- 

 tiful in soft clays and argillaceous schists, much less good in sandstones ; 

 yet serviceable impressions are sometimes found in tolerably coarse-grained 

 conglomerates. 



In many cases the remains which were to be inclosed had interior 

 cavities of their own, as is commonly the case with stalks, fruits, and seeds. 

 These cavities became also filled with the enveloping material, and a cast 

 was produced, the surface of which shows the sculpturing on the outer 

 bounding surface of the original cavity. The space between the cast and 

 the mould is usually filled with coal ; it may be hollow through previous 

 decay of the part of the plant, but this must be regarded as a rare con- 

 dition in the preservation of the remains. On every heap of debris from 

 the Coal-measures are found the casts of Calamites in abundance, in many 



1 Grand' Eury (1). 2 Blum (1). 3 Berendt (1). i Goppert (21) (Goppert und 



A. Menge), vol. ii, Introd. p. vL 



