SHOWING STRUCTURE, FROM THE RHYNIE CHERT BED, ABERDEENSHIRE. 763 





Continued. 



D 



ft. 

 



in. 

 3 



8 



Silicious band with thin sandstone layer at top and base with plant remains. 



C 







3 



7 



Fine light grey silicious sandstone. 



(■ 







9 



'{ 



Band of bedded silicified peat formed of Rhynia, with stems usually much decayed. 

 At top occurs a thin bed of silicious sandstone. 



(•■ 







6 



5 

 4 



Cherty sandstone with carbonaceous matter. 



• A " 



1 



3 



3 

 2 

 1* 



Silicious sandstone with carbonaceous matter. 

 Highly silicious sandstone with Asteroxylon. 



Thick bed of impure peat with Rhynia and Asteroxylon. Stems generally much 

 decomposed. 







2 



2 



1 













Grey clay. 



White plastic clay, greenish tint and rusty spots, bedding obscure but more distinct 



near bottom. 

 Clay or clayey shale, not so light in colour as that above. 







Rhynia extends throughout the whole section. Asteroxylon has only been observed 

 up to the present in bed A". 



It is not our sphere to treat of the detailed geology of the Rhynie area ; that will 

 be done by other and more competent writers. As intimately connected with the 

 petrifactions which have been placed in our hands for description, it is, however, 

 necessary to make some remarks on the nature of the chert band in which 

 they occur. 



Our material has consisted of a complete set of specimens taken from the chert 

 band, lettered and numbered as noted in the first and third columns of the section 

 given above. In addition, some of the loose specimens have yielded most valuable 

 information. The chert is much jointed and fissured, and when fresh is of a blackish 

 or dark grey colour in which, when visible, the plants are only indicated by darker 

 spots or streaks. Specimens naturally weathered sometimes assume a light buff 

 colour, and the plant-remains are clearly exhibited (PL II, fig. 2). When blocks are 

 treated with a weak solution of hydrofluoric acid, which etches the surface and brings 

 out more or less distinctly the structure of the chert, the plant-remains are also 

 rendered more visible (PL I, fig. 1 ; PL II, fig. 5). 



The blocks themselves and the numerous microscopical sections studied prove 

 that the whole chert zone was originally formed of a series of peat beds which, 

 during their formation, had been subject to periodic inundation, when thin layers of 

 sand were spread over the surface. Each bed of peat appears to have a thin layer 

 or bed of sand at its top. 



Several of the isolated specimens have shown the plants growing vertically from 



* This column gives the original numbers of the specimens as collected. 



