124 G. W. Card—FlcxihiUty of Rocks. 



but a little thicker (-r;j-incli), bent under pressure through a vertical 

 distance equal to somewhat less than half the length of the strip ; 

 the limestone gave slightly higher results, but was somewhat thinner 

 (1-5 mm.). In slabs of greater thickness, however, the superior 

 flexibility of the Itacolumite is very marked; thus Mr. Oldham found 

 a piece 17 inches long by '75 inch thick bent through 7 inches of its 

 own weight, while in slabs of limestone of 5 mm. thickness flexibility 

 becomes very slight. They agree also in a decrease of flexibility 

 accompanying increase of thickness. In both cases the occurrence 

 of flexible portions is very local ; this has already been referred 

 to, but it may be mentioned further that fine-grained, bedded, non- 

 flexible limestones occur in the neighbourhood, and it would be 

 interesting to know whether these non-flexible beds possess the 

 internal structure described above. It is, however, in internal 

 structure that the resemblance is most marked, both exhibiting a 

 number of vacant spaces accompanied by an interlocking of the 

 constituent crystalline grains. Flexibility would thus seem to arise 

 from similar causes ; we have room for movement afi"orded by empty 

 spaces, the result of solution of carbonates in the one, and of the 

 decomposition and removal of patches of felspar in the other ; while 

 the direct cause of bending is the interlocking of the grains. 



It is well known that a distinct sound is heard when flexible sand- 

 stone is bent ; the limestone does not give rise to any sound that 

 is audible, but, from the inferior hardness of calcite, as compared 

 with quartz, this is no more than might be expected. 



Lastly, there is the occurrence of the calcareous rock at Chaiii. 

 This may, indeed, be regarded as a connecting link between flexible 

 Itacolumite on the one hand and flexible limestone on the other. 

 It is not only that it contains a certain proportion of carbonate of 

 lime ; that might be quite a matter of detail ; but from the passage 

 quoted above it would seem that the calcite plays an important part, 

 forming interlocking aggregates, and affording the space necessary 

 for movement by its solution. Moreover it is described as. a common 

 sandstone, the grains of quartz being somewhat rounded ; this would 

 seem to emphasize the presence of the calcite, as it is not clear what 

 part such quartz can take in efi'ecting movement. 



In conclusion, now that a number of rocks are known to 

 exhibit the property of bending without fracture, in each case the 

 phenomenon being no more than a natural concomitant of certain 

 phases of alteration, the undesirability of giving distinctive names to 

 the different varieties will be at once apparent. Indeed, there seems 

 no reason why many other varieties should not also occur, although, 

 from the nature of the conditions to be fulfilled, we cannot expect 

 to find flexible beds in considerable quantity. 



I have already acknowledged ray indebtedness to Prof. Judd, and 

 it only remains to state that this work has been carried out in the 

 Geological Laboratory of the Eoyal College of Science. 



