1871.] CARPvUTHERS SUPPOSED VEGETABLE FCSSIIS. 445 



but is the material of the bed polished in some way — and, furthei', 

 that the detached fruit-like body has many layers of such glazed 

 surfaces, subparallel to each other, and all separated by the ordinary 

 substance of the bed, which thus makes up the body of the so-called 

 fruit. The glazed laminse originate from the somewhat granular 

 nucleus. There frequently occur on the same hand-specimen small 

 patches of similarly glazed surfaces with irregular outlines (PL XIX. 

 tig. 12), to which the name Slickenside has been incorrectly applied ; 

 this term is properly employed and should be restricted to designate 

 the smooth and poHshed appearance produced by enormous friction 

 on the contiguous surfaces of a fault. The structures, however, in 

 shale, to which the name is applied are confined to the stratum in 

 which they occur, and never pass from one surface to the other ; 

 they occupy all positions in the bed, and are isolated or sometimes 

 united at angles more or less acute ; the polished surfaces are fre- 

 quently crumpled and waved. All these points in their structure 

 show that they are not due to a force external to the bed, and that 

 the polishing has not been produced by the sliding backwards and 

 forwards of the one surface on the other. Dr. Fleming carefully 

 investigated these appearances, and proposed what appears to be a 

 very satisfactory explanation of their origin. He believed them to 

 have been produced in cavities in a comparatively soft plastic matter 

 by the presence of water or gas contained in the cavities, and that the 

 specular aspect was the casting or impression of the fluid substance *. 

 These limited slickensides, or as I would prefer to call them. Jluid-casts, 

 occur in rocks which have been at one time or other in a more or 

 less viscous or tenacious condition ; they are found in argillaceous 

 rocks of aU ages. So also are the fruit-like bodies which I have 

 described ; I have obtained them from the shale-beds of the Coal- 

 measures in England, Wales, Scotland, and North America, and from 

 the Newer Tertiary clays of Ulm, Wiirttemberg ; they have been 

 figured from the Coal-measures of Germany, and from the Permian 

 rocks of Saxony. The granular nucleus which is found in the centre 

 of these fruit-like bodies, was, I believe, the source of the gaseous 

 substance which has left its impress on the glazed surface. This 

 nucleus appears to me to have been a crystalline concretion, which 

 subsequently decomposed ; and the gas then given off spread outwards 

 as it was produced in the planes of stratification, this being the 

 direction of least resistance. 



These fluid-casts were flgured by Ehode in his * Beitrage zur 

 Pflanzenkunde der Vorwelt' (1820) pis. vi., vii., ix., and x. The 

 first two plates give a faithful representation of the objects ; but a 

 little play is given to the imagination in plate ix. ; and its unfettered 

 operation is seen in the tenth plate, where the different polished sur- 

 faces are converted into the petals of flowers, and the whole are 

 associated with foliage for which a species of Veronica has apparently 

 supplied the design. 



The two following species have been based on these fluid-casts : — 



* " Dr. Fleming on the straetural cbaracters of Eocks," Proc. Eoy. Soc. Edin. 

 vol. iii. p. 170. 



