BRITISH CARBONIFEROUS PLANTS 143 



as concretions in the seams in which they are now found, 

 and have not been derived from other sources." They instance 

 several localities and seams in which they occur. In the 

 formation of the coal balls " the sea-water played the principal 

 part in the process of preserving and petrifying the plant- 

 remains now found in coal balls, the calcium and magnesium 

 sulphates being reduced from the sea-water by organic carbon 

 liberated by the decay of the plants." Some of these conclu- 

 sions are opposed to those held in other quarters (37). 



Carboniferous Impressions 



Turning now to the studies of Carboniferous Impressions 

 and Fossil Floras, it may be well to take for review a some- 

 what longer period extending back to the year 1900. We 

 still await eagerly the appearance of Dr. Kidston's Monograph 

 of the Carboniferous Flora of Britain. The need for a systematic 

 and standard work of this nature has been urgent for many 

 years past. In this respect we have been much behind other 

 countries. The fine series of Fossil Floras from the various 

 coalfields of France, published in the Etudes Gites Mineraux de 

 la France and other large quartos, has no parallel in Britain. 



Special studies of certain genera or species, preserved as 

 impressions, have been remarkably few in recent years, apart from 

 the fructifications of the Pteridospermese, such as Rhabdocarpus, 

 Crossotheca and Lagenostoma referred to in my previous review 

 in Science Progress (6). Kidston (26) has contributed a full 

 account of " Carboniferous Lycopods and Sphenophylls," in 

 which a new genus from the Mountain Limestone of West- 

 morland, Archceosigillaria, is described, and a full account of 

 Omphalophloios is also included. 



Bernard Smith (57) has also discussed an interesting 

 Lepidodendroid stem from the Middle Coal Measures of 

 South Staffordshire, in which the leaf-cushions are distant from 

 one another and separated by broad bands of striated bark. 



Illustrations of the flora of the Carboniferous period have 

 been published by Kidston (28), consisting of twenty-eight 

 plates of Carboniferous plant impressions with explanations ; 

 quite recently the present author (10) has prepared a little 

 volume containing sixty photographs of typical Upper Carboni- 

 ferous plants. 



