24 INTRODUCTION. 



according to Grand' Eury was produced. The stumps are often hollow, 

 reduced to the rind, and filled with a stony mass in which impressions of 

 parts of other plants are often found. To explain these peculiar conditions 

 Grand' Eury supposes that the temporary raising of the level of the water 

 in the basins of accumulation flooded the flat swampy forest-ground far and 

 wide, and that the trees were killed by the inundation and became rotten and 

 at last fell to pieces, their stumps only remaining erect beneath the water. 

 Such behaviour is quite conceivable, if we take into account the small 

 development of wood and the succulent nature of the rind in the trees of 

 the Carboniferous period ; and that something of the kind does take place in 

 warm climates I was able to satisfy myself in the Botanic Garden at Buiten- 

 zorg, where a colossal palm-tree, which had died after developing its terminal 

 inflorescence, broke up and fell in pieces before my eyes with a startling crash. 

 If the raising of the level of the water was followed by an irruption of the 

 adjacent sea into the lagoon, and this might very well happen when the land 

 was so low and flat as in that era, then the coal-forming basins would be 

 overlaid by inorganic deposits ; and these deposits would envelope the tree- 

 stumps on the margin of the basin and fill the cavity inside them, and by 

 local extension of the phenomenon might accumulate large masses of matter 

 or form thin beds of stone, or bury the whole formation if they were on 

 a still more extended scale. If the layers then lost their water, they might 

 harden and pass into the condition of coal. We recall to mind the state of 

 the timbers which in the mine were soft and plastic, but as they dried were 

 found to have been converted into coal with a conchoidal fracture. 



To the above account of the origin of the incrustations of which coal- 

 seams are an example of the grandest kind, we may here append a brief 

 description of the mode of formation of true petrifactions. These are dis- 

 tinguished from incrustations by being formed only when the object to be 

 petrified is permeated by dilute solutions of the petrifying substance. The 

 compounds which usually cause petrifaction are apt to produce incrustation 

 only when they are in the form of a concentrated solution. On this point 

 we may appeal to the incrusting spring of Carlsbad, to the incrusted 

 thorns in the drying-houses in our salt-works, and to the siliceous sinter of 

 Iceland and New Zealand. Amber only, which, as has been already said, 

 is an agent partly of petrifaction, partly of incrustation, is an exception 

 in this respect. As resin from Conifers- of the Tertiary period it first 

 enveloped any objects which it encountered, and if these were capable of 

 absorbing resin they were gradually and slowly permeated by the envelop- 

 ing substance, just as microscopic preparations are permeated by canada- 

 balsam. Succulent objects on the contrary were only enveloped by the 

 resin, and as the water evaporated it often formed vesicular spaces on and 

 around them, which were preserved as the resin hardened into amber. For 

 that amber in spite of the difference in its chemical character is, as is here 



