BY E. G. HOGG, M.A. 135 



This view of the connectiou between the decomposition 

 and flexibility of the sandstone is, to a certain extent, borne 

 out by Mr. Tuomey in his Report on the Geology of S. 

 Carolina. He observes that the itacolumite of that state 

 "passes even in the same mass into compact quartz, to bft 

 distinguished from common quartz only by its stratified 

 structure," and that " the passage from the arenaceous to the 

 compact variety is gradual, and it is in this passage that it 

 assumes the form of itacolumite" (flexible sandstone). 



It must be noticed that the term itacolumite has two 

 different significations ; it is with some fyiiters " flexible 

 sandstone," with others the bed-rock in which " flexil>le 

 sandstone " occurs. 



It would ajDpear that so far as the field relations are 

 coucerned — though more evidence on this point is much 

 to be desired — itacolumite only becomes flexible when it has 

 undergone a certain amount of decomposition, probably due 

 either to weathering, or to the percolation of water or other 

 solvent. Such weathering or solvent action may remove, 

 either in toto or in part, certain of the original constituents (^f 

 the rock. Of course, as a result of chemical combination, 

 these constituents may be replaced, to a more or less extent, 

 by other bodies. 



It is worth noticing that so far as our knowledge on the 

 subject goes, flexible sandstone only occurs in metamorphosed 

 deposits, which are undoubtedly of very ancient origin. 



B. 



In this section of the note I mast acknowledge how much I 

 am indebted to the paper of Mr. Oldham, previously referred 

 to. I now propose to give a digest, mainly drawn from Mr. 

 Oldham's pa,per, of two theories brought forward to explain 

 the peculiar properties possessed by flexible sandstone. 



It seems best to refer to the generallv accepted theory, i.e., 

 the theory found in recent times in many extensively pur- 

 chased treatises and manuals on gt^ology. This theory would 

 ascribe the flexibility of itacolmuitic sandstone to the talc, 

 chlorite, and mica stated to occur in it. It is only fair to 

 notice that the partisans of this older view were unacquainted 

 with the modern methods of petrological analysis. This 

 older view of the cause of flexibility can be traced to Von 

 Eschwege, to whom is due the fanciful name of itacolumite. 

 But apart from the difficulties depending on the physical 

 properties — in the matter of elasticity — of mica, it appears 

 quite clear from Mr. Oldham's paper that flexibility is 

 exhibited bv the itacolumite, even when mica is absent, or is 

 quite subsidiary. If the cause of the flexibility lie in the pre- 

 sence in the slab of flakes of mica, chlorite or talc, whose planes 

 are parallel to those of the laminations of the slab, it is diflfi- 



