108 TIIK AMKUICAN MONTHLY [Aj^ril, 



sure, aiiiotl bv scct)iul;uv (>ut«;to\vths of quart/, optically contin- 

 uous with the orijjinai jjrains, till it is now composed ot" inc<ju- 

 larlv-shapcd j^ianulos otcjuart/. for the most part in close contact 

 witli each other, but intermixeil with a small proportion of a 

 telspathic )>aste. This paste yields more readily to the action of 

 weather than quart/., and. thou<jh weatherinj; iloes doubtless also 

 take place alonjj; the junction siuf'aces of the individual grains of 

 quart/, the disinteijration of the rock appears to result almost en- 

 tirely iVom the decomposition of the felspathic paste. In such a 

 rock the development of flexibility will depend on the jjroportion 

 and ilistribution of the felspathic paste. If this be absent or onlv 

 present in small proportions, decomposition will not extend to 

 anv depth, and there will be a mere film of decomposed stutVon 

 the surface of the undecomposcd rock ; if it is too evenlv dis- 

 tributed, the iuilividual grains of quartz will not be in sufhcientlv 

 intimate contact with each other, and the rock will weather into 

 a line sand, e.isily washed away: if finally it should be suitably 

 ilistributed. but too great in amount, the voiils left bv its removal 

 will be so large that the quartz aggregates will not interlock with 

 each other. The number of conditions that must be fulfilled ac 

 counts satisfactorily for the raritv of flexible samlstone. and for 

 its capricious distribution in rocks that have to all appearances 

 the same composition and structure. 



In 1S71 Mr. Fedden found at Charli, south of the Penganga 

 river in Berar, a rock which exhibits the same sort of flexibility 

 as that of Kaliana, but differs widely from it in every respect ex- 

 cept that it is now, what the other once was, a sandstone. In- 

 stead of being composed almost entirely of quartz and owning its 

 cohesion to the metamorphism it has undergone, it is an ordinary 

 unmetamorphosed calcareous sandstone, at first sight not remark- 

 able for anvthing but its softness, and the large proportion — over 

 3t; per cent. — of carl^onate of lime it contains ; but a closer exam- 

 ination will show that the calcareous cement has become crystal- 

 lized, and that the rock is now in reality composed of crystals of 

 calcite some ^J^-inch in diameter which include the odd 65 per 

 cent, of quartz and other granides as so much extraneous matter. 

 Microscopic inclusions of extraneous matter in crystals are com- 

 mon enough, and often form a considerable proportion of their 

 total bulk, and the celebrated case of Fontainebleau sandstones, 

 where the calcite crystals contain 90 per cent, of sand, shows to 

 what an extent this can be carried. In the case of the Charli. 

 rock, the large proportion of crystalline structure of the cement 

 has had important results. It is a well-established fact that when 

 a crystal is attacked by a solvent it is not uniformly acted f)n, 

 but that solution acts more rapidly along certain planes which 

 penetrate the crystal in various directions. In the case of the 

 Charli rock this has taken place, and the numerous surfaces of 

 contact between the crystalline calcareous cement and the grains 

 of sand have been so many more surfaces of weakness along 



