362 SCIENCE PROGRESS. 



In some French coals there are distinct signs that the rock 

 is little more than a thoroughly carbonised mass of strap- 

 shaped Cordaites leaves. A careful naked-eye inspection of 

 some coals reveals the existence of small compressed 

 circular or elliptical bodies which, on isolation and micro- 

 scopical examination, are found to show a very striking 

 resemblance to the macrospores of some recent pterido- 

 phytes. The marked similarity of the fossil and recent 

 forms has been demonstrated by Williamson and other 

 writers ; it is very clearly shown in some figures given by 

 Kidston and Bennie in a paper dealing with Carboniferous 

 macrospores. 



The microscopic investigation of coal is necessarily at- 

 tended with some difficulty owing to the opaque nature of 

 the material. Some observers have adopted a method of 

 examination by means of specially prepared semi-transparent 

 sections ; others prefer to treat pieces of coal with potassium 

 chlorate, nitric acid, and other reagents, in order to isolate 

 the plant tissues. Suggestions as to manipulation and the 

 preparation of sections will be found in the contributions of 

 Glimbel, Dawson and others. 



The great pioneer work of Witham of Lartington on 

 The Internal Structure of Fossil Vegetables, includes a short 

 description and a few figures of microscopic preparations of 

 cannel and other coals. Shortly after the publication of 

 Witham's results, Hutton recorded the occurrence of some 

 light wine-yellow coloured material in the cavities of plant 

 cells, as seen in thin sections of certain kinds of coal; this was 

 regarded as apparently a bituminous substance, which he 

 found to be readily expelled on heating. These observations 

 of Hutton are of special interest in connection with some 

 startling results recently published by MM. Renault and 

 Bertrand on the boghead coals of Central France, Scotland, 

 and Australia. In 1838 Link gave some account of the 

 microscopic structure of peat, lignite and coal ; he figures 

 various fragments of plant tissues, and small resinous orange- 

 coloured bodies, the nature of which he leaves undecided. 

 He regards coal as the peat of a former geological age. In 

 1857 Bennett made a detailed examination of the structure 



