INTRODUCTION. 31 



up together in it in the state of confusion in which they were deposited. 

 That they were in a soft and macerated condition is evident from their 

 being traversed in all directions by a luxuriant growth of fibres of Stigmaria, 

 and thus rendered useless for purposes of investigation. These phenomena 

 are so extremely important for determining the anatomical character of the 

 vegetable types of the Carboniferous formation, that it will be well to dwell 

 a little longer on them and on their occurrence. 



Deposits of this kind are seldom found in the silicified state. Putting 

 aside the hornstones of the district of Chemnitz, in which the state of 

 preservation is not usually of the best, we have really nothing to mention 

 but the often-quoted dark brown siliceous fragments of Grand' Croix near 

 St. Etienne, in which the parts of the plants are often so wonderfully well pre- 

 served, that Renault was able to determine from them a large number of the 

 most important facts relating to the structure of the leaves, flowers, and seeds 

 of the inclosed plants. These stones are sharp-angled fragments of different 

 sizes which have never been rolled, and are associated with a variety of 

 other objects to form a conglomerate. Many of them had been set free by 

 weathering and lay scattered over the fields ; but they have now been 

 collected, as far as was possible, and brought to Paris, for there was reason 

 to fear that they would soon disappear altogether by being used for industrial 

 purposes. It is evident that they originally formed a connected stratum 

 which was broken up, its remains only being preserved in the conglomerate. 

 The horizon of the strata from which these fragments came lies ac- 

 cording to Grand' Eury 1 between the coal-bearing strata of St. Etienne 

 and those of Rive de Gier ; it belongs to the uppermost division of the 

 Coal-measures. 



While the vegetable remains preserved in siderite are usually single speci- 

 mens and are inclosed in geodes of clay iron-stone, calc-spar and dolomite 

 occur in many places as the petrifying agents of entire deposits, after the 

 manner of the siliceous fragments of Grand' Croix. We have known for some 

 years 2 that certain seams in the great coal-fields of Lancashire and Yorkshire 

 contain irregular roundish masses, large and small, which are the petrified 

 portions of the seam. The excellent researches of Williamson and Binney 

 rest essentially on specimens collected from these petrifactions near Halifax 

 and Oldham. But the induration in the substance of these nodules, which 

 consist principally of calc-spar, is very much less than that shown by the 

 siliceous pebbles of Autun in favourable circumstances. The seams which 

 contain them belong to the lowest beds of the Coal-measures of central 

 England ; they occur a short distance above the Millstone Grit, and alternate 

 with certain characteristic hard beds filled with Goniatites and Aviculopecten 



Grand' Eury (1). 2 Binney (1), i, p. n. 



