Geology and Mineralogy. 291 



levels between the higher ground and the sea. The water round 

 their roots was brackish or salt, as is the water of the mangrove 

 swamps to-day, and into its quiet pools and shallows twigs and 

 branches, stems, leaves, and fruits fell or were blown. These 

 fragments sank into the mass of debris already saturated and 

 were there shut out from the atmosphere and preserved by the salt 

 water in which they lay immersed. Parts of the plants decayed 

 and thus liberated the organic carbon, which began its slow task 

 of reducing the sulphates and depositing them as insoluble car- 

 bonates. This process continued long without the entry of 

 impurities or the deposition of anything but plant remains, and 

 the rootlets of the living plants wandered among the dead ones, 

 finding their way even through the heart of their stems or seeds. 

 " All the time the land was slowly sinking, and when several 

 feet of debris had accumulated the level sank more abruptly till 

 the plants were well submerged and the place where the forest 

 trees had lived was covered by the waters of an arm of the sea. 

 Over them was deposited fine mud, with the shells of Goniatites 

 and Aviculopeeten, which lived and died in the waters. The 

 plant masses below were continually withdrawing the sulphates 

 of lime and magnesium from the sea water and depositing them 

 as carbonates round the many centres started among the frag- 

 ments of plants. The supply of salts was inexhaustible, for new 

 water mingled continually with the old and brought fresh 

 sources of mineral to petrify the plants. Thus in the heart of the 

 masses of coal were formed large and small concretions of 

 carbonate, some regular as balls and very large, others minute 

 and uniting together to form wisps or sheets of stone lying in 

 the coal. 



"In the sea above, the currents carried fragments of plants 

 from the neighbouring land, brought by the streams from the 

 higher ground. These sank in the muddy floor and were grad- 

 ually crushed by the silt collecting above them, till they were 

 flattened as impressions in the beds which afterwards formed 

 shales * * *. 



" These drifted plants, whether their fate was to be enclosed in 

 the preserving nodules or to be crushed into the shales, had prin- 

 cipally come from regions different from those which had pro- 

 duced the half-formed coal now lying immediately below them. 



" Slowly they too were covered by the fine deposits which col- 

 lected gently over them, until the sea bottom rose again to form 

 a new land. All this time the plants w r ere preserved in the coal 

 balls without disturbance or hurt, and although the coal-forming 

 debris had been pressed down into coal w T hich was now but a foot 

 in thickness, they remained uncrushed in their original form. 



•I* *i* *T* TF? *T* V 



" Thus, the i coal balls ' in the coal are the relics of a forest 

 which grew quietly in the swamp in the place where they are now 

 found, while the plants in the shales and in the roof nodules 



