1893.] MlCKOISCOl'lCAL JOL'U.NAJ.. I(i7 



Flpxiblp Sandsfonc. 



liv R. U. OLDHAM, 



CALCUTTA, INDIA. 

 [Abstracted from un address before the Microscopical Society.] 



Tlie cause of tlic flexihilitv is evident at once if the rock is ex- 

 amined nnder tlie microscope ; in fact, it mav be detected in the 

 coai"ser-<;iained specimens witli no more poweifid maj^nifying 

 power than is fmiiished hv a C<)ddin<jton lens. If the rock is ex- 

 amined under a low power by retlected liglit, it will be seen that 

 the rock is of a cavernous nature and composed of irrej^ular- 

 shaped fraorments, each of which is loose and can he moved back- 

 wards and forwards slightlv with a nectlle point; in fact, the rock 

 is composed of a number of granules, each perfectly detached 

 from its neighbors, and each possessing a certain amount of free- 

 dom of movement, owing to tiie intervening space. It is quite 

 obvious that a rock of such constitution would have just such a 

 freedom to alter its shape, within certain limits, and not bevond 

 them, as is possessed by these specimens, and all that remains to 

 be explained is how these separate granules manage to hold to- 

 gether. 



Turning now to the transparent section of the same rock it will 

 be seen that the outline of the individual granules is very irregular, 

 and occasionally projections on one granule will be seen inserted 

 into recesses in an adjoining one. In fact, the rock resembles one 

 of those toys where a picture pasted onto a thin piece of wood has 

 been divided up bv sinuous cuts of a fret-saw into a number of 

 irregular-shaped pieces. When these are properly fitted together 

 again the slab and picture hold together as a whole, and can be 

 pushed or pulled about on the surface of the table, but it is no 

 longer solid, and within certain limits can be stretched, short- 

 ened, or have its shape distorted, just as is the case with our flex- 

 ible sandstone. The only difference is that the projections and 

 recesses, instead of lying all in one plane, are in every direction 

 and on all sides of the granules composing the rock ; hence it is 

 that in the thin section we only occasionally see an actual case of 

 interlocking, for only those projections wdiich lie in the actual 

 plane of the section remain, all the others having been ground 

 away. 



How did this structure arise.'' The first thing to notice is that 

 the flexible stone is essentially a product of the decomposition of 

 rock which exhibits no such character. This is certainlv the case 

 as regards the Indian specimens, and the same has been noticed 

 in the case of both the North and South American localities, 

 where a similar rock has been observed. At Kaliana the unde- 

 composed condition of the rock is a hard glassy cpiartzite, a thin 

 section of which is exhibited, and it will be seen that the rounded 

 grains of sand, which formed the rock in its original condition, 

 have changed their shape under the influence of heat and pres- 



