122 Q. W. Card—FlexiUUtyofRochs. 



and flexible portions, witliin a distance of a few centimeti'es, and in 

 exactly the same relative position in the bed." The author's con- 

 clusion is that flexibility is a ^j/mse of xveatliering. Tuomey came to 

 the same conclusion with regard to the Soutli Carolina stone, but 

 Leibner differed from him. 



Miigge describes the Delhi stone. There is a very little mus- 

 covite, but so small a quantity that it cannot possibly give rise 

 to the flexibility. A small amount of clayey matter is present, 

 not surrounding the quartz grains, but in patches which are not 

 sufficient to fill the interspaces ; the quartz is therefore much clearer 

 than in ordinary sandstones, and the grains are in direct contact 

 with one another ; moreover, the grains have a very irregular out- 

 line (comparable to Babel-quartz), being ver^' different in appearance 

 from those of common sandstone. When examined in thin sections 

 by means of polarized light, the quartz grains are seen to be hooked 

 together. This interlocking accounts for the grains holding together, 

 and at the same tinie allows of a certain amount of movement taking 

 place, space for movement being afforded by the decomposition of 

 the clayey patches. In this way the author thinks the flexibility 

 can be explained. Dealing briefly with the Brazilian stone, he 

 shows that the quartzes present an appearance almost identical with 

 the Indian ; there is very little clayey material, so that a section is 

 almost as clear as water ; while muscovite occurs only in small 

 quantity, and in flakes much too short to envelop the quartz-grains. 

 It is suggested that the structure of these rocks originated by a 

 partial removal of the cementing matei-ial ; the quartz-grains then 

 resumed their growth, but the supply of material failed before the 

 interspaces left on the removal of the clayey matter were completely 

 filled. 



Mr. Oldham, also dealing with the Delhi specimens, arrived 

 independently at the same results. In India, as in Brazil and in South 

 Carolina, flexibility is correlated with decomposition. Examined 

 under the microscope by reflected light a number of quartz- 

 aggregates, separated by vacant spaces which appear to be ramifying 

 fissures, are seen. These aggregates can be moved by a needle 

 without displacement, the movement being the result of the grains 

 being hinged together, a projection from one fitting into a depression 

 in another. He also notices the occasional presence of felspathic 

 paste, which, by its relative abundance and mode of distribution, 

 determines the degi'ee of flexibility that will be possible on its de- 

 composition and removal. Having regard to the subject of this paper, 

 one of the specimens described by Mr. Oldham is of special interest. 

 It is a variety from Charli, south of the Pemganga River (Berar). 

 "An ordinary soft sandstone of rounded grains of quartz, with a 

 little felspar, held together by a cement of carbonate of lime, 

 which forms 35 "9 per cent, of the whole mass.^ Here there is no 

 comparatively soluble material whose removal leaves the rest of the 

 rock as a mass of irregular aggregates interlocking with each other, 

 for on removal of the cement, b}' solution, the rock falls into sand. 

 ' The italics are mine. 



