402 MR. B. THOMPSON ON LANDSCAPE MARBLE. [Aug. 1 894, 



While the stone now called Landscape Marble was being formed 

 there were very frequent alternations of light-coloured and darker 

 matter deposited (7-9), and occasionally a dark layer of greater 

 thickness than usual was formed, with the apparently inseparable 

 accompaniment of arborescent markings above it (4, 8) ; if two such 

 unusually thick layers occur there are two landscapes (5). Three 

 landscapes may and do occur, but I have never seen a specimen. 



The connexion of the arborescent markings with the dark layer 

 from which they spring may, therefore, be regarded as beyond doubt, 

 though if other proof were needed it would be found in the facts 

 that they are of the same colour ; of the same lustre (11), which is 

 different from that of the matrix ; and of the same chemical com- 

 position and crystalline form (11, 12). 



That the arborescent markings originated from the dark layer, and 

 not the latter from the former, must be obvious, from the following 

 considerations : — All the markings start from the dark layer, 

 whereas they finish anywhere, some only at half the height of 

 others (see fig. 1, p. 395) ; the narrowest portion is downwards 

 (4), whereas the opposite would be the case if the source had been 

 above. But the most conclusive reason of all is the invariable 

 lifting of the matrix contiguous to the dark markings (8). 



The material of the dark bands and arborescent markings must 

 have been either more plastic than the matrix, or of a less dense 

 matter, to have allowed itself to be squeezed or lifted from its 

 original bed through overlying layers (4, 8). I think it was actually 

 both less dense and more fluid, for not only was it lifted through 

 comparatively heavy inorganic material, but when it reached the 

 surface it spread out in all directions, and produced exceedingly thin 

 films of dark matter which completely roofed in the arborescent 

 marks (9) ; see also fig. 1, p. 395. 



The dark matter could not have been a coloured fluid merely, for 

 although the matrix of the stone admits of staining, since it can be 

 bleached by weathering (7, 9, 12), no staining has occurred, the 

 outer boundary of the markings being sharply defined ; in fact, the 

 markings are distinctly darker along their outer boundary than 

 anywhere (11), except the spots in the spotted form (12), whereas 

 with ordinary staining the reverse would be the case. 



It would appear, therefore, that the original material of the dark 

 markings was semi-fluid, and contained finely divided dark matter, 

 such as carbon or oxide of manganese, disseminated through it. 



That carbon and not oxide of manganese (15) was the darkening 

 matter appears tolerably clear, for the following reasons : — The 

 dark parts are readily bleached by a blowpipe flame (15) ; in one 

 specimen darker spots are very unequally disseminated through 

 these parts (12); I have experimentally shown that bubbles of 

 carbonic-acid gas will lift and disseminate finely-divided carbon 

 from a layer covered with fine sand, whereas they would not lift 

 oxide of manganese ; and, lastly, carbon fits in much better with all 



