280 PROCEEDINGS OF THE AMERICAN ACADEMY. 



these objects, resulting from age-long pressure, cooperating with the 

 softening effect of gradual decay, they are so thin that they rarely 

 appear in more than two thin horizontal sections, more rarely in three. 

 By the study of serial sections it was perfectly clear that the supposed 

 Alga, P'da kentuchjana of Renault, and the obvious spores of vascu- 

 lar cryptogams, found in the same sections of coal, were different ap- 

 pearances presented by the same object. When only the free surfaces 

 of the spores appear in the plane of section, as is more often the case, 

 then their roughened exterior presents a mottled or alveolar appear- 

 ance, which has been interpreted by a number of European observers 

 in this and parallel cases as representing the bodies of gelatinous colo- 

 nial Algae. When the angular or rotund aspects of the spores appear 

 in section, their real nature is perfectly obvious. The error made by 

 those who have been able to study only a few comparatively thick sec- 

 tions of the coals in question, results from not correlating the two sorts 

 of appearances ; an error scarcely to be wondered at from the nature 

 of the preparations at their disposal. 



The Structure of Scotch Boghead Coals. 



The microscopic structure of the bogheads of Scotland is of par- 

 ticular interest because coals of this general type were earliest recog- 

 nized here and the classic example Torbanite from Torbane Hill may 

 be regarded as the original boghead, from the standpoint of scientific 

 recognition. Through the kindness of Captain Baird G. Halberstadt, 

 F. G. S., of Pottsville, Pennsylvania, I have had the opportunity of 

 examining authentic material of a number of the Scotch coals of 

 this group. 



Figure 16, Plate 3, shows part of a section parallel to the planes of 

 layering in a boghead coal, so called, from the Armadale deposits, Bath- 

 gate, Linlithgow, Scotland. The magnification, which is moderate, 

 reveals the presence of a number of bodies of a nature similar to 

 Pila kentuckijana, described in previous paragraphs. Like P'da 

 kenUicJcyana, they have an alveolar mottled appearance in certain 

 planes of section, while in others they reveal a central cavity circular 

 or angular in contour, as the case may be, and finally in some cases the 

 bodies in question are grouped together in obvious tetrads or reveal 

 the triradiate face characteristic of most Lycopodineous spores. All 

 these conditions are revealed in the various parts of Figure 16, as may 

 be ascertained by the use of a hand lens. Near the middle line of the 

 figure above and below may be seen tetrads in various planes of section. 

 Two of these in the upper and lower region of the photograph are par- 



