134 



NOTE ON ITACOLUMITE OR FLEXIBLE SAND- 

 STONE. 



By E. G. Hogg, M.A. 



A. 



The existence of flexible sandstone appears to have been 

 known of since 1780, when specimens were brought to 

 Europe from Brazil bj the Marquis of Lavradio, Viceroj of 

 Rio de Janeiro. The bed-rock in which the flexible sand- 

 stone occurs was found by Von Eschwege to be largely 

 dereloped near Mt. Itacolumi in the State of Villa Rica, 

 Province of Mina Garaes, Brazil, and is described by him as 

 a fissile sandstone containing plates of talc, chlorite, and 

 mica. This rock contains a little gold, and has been shown 

 by Heusser and Claraz to be the parent source of the Brazi- 

 lian diamond. The beds generally rest on the crystalline 

 schists and frequently pass into conglomerates. According 

 to Fr. Hartt (Geology and Physical Geography of Brazil, 

 1870) the bed-rock is probably an altered Lower Silurian 

 formation, while Prof. 0. A. Derby classes it as of Huronian 

 age. In this bed-rock the flexible sandstone occurs in some 

 abundance; it is distributed in such a manner as to point 

 strougly to the conclusion that the sandstone is only flexible 

 when it has been considerably metamorphosed. Professor 

 Derby* states that on one side of a fissure the rock may be 

 often found without any trace of flexibility, while on the 

 other it is laminated and flexit'ie. He concludes that flexi- 

 bility is not an oi'iginal characteristic of the rock, but is a 

 " phase of weathering " or decay brought about by percolating 

 waters. 



Mr. R. D. Oldham, F.G.S,, Director of the Indian Geolo- 

 gical Survey, f has discussed at some length the occurrence 

 of flexible sandstone at Kaliana, near Dadri in Jhind. [It is 

 probable that the specimen exhibited by the Lord Bishop of 

 Tasmania came from this locality.] Mr. Oldham states : " at 

 Kaliana the flexible stone occurs on a hill composed of 

 vertically bedded glassy quartzites : it is confined so far as 

 my investigations and enquiries went, to one single spot 

 where, for about 20 feet across the strike, and for about 

 30 yards along it, the rock has become flexible; near the 

 margin of this area the flexible stone passes downwards into 

 the ordinary quartzites, but in the centre the decomposition 

 had extended downwards to the floor of the quarry, a depth 

 of fully 15 feet; here, too, the rock was much softer, more 

 decomposed and flexible than near the margin." 



* Ainer Journal of Science, Vol. XXIII. (1884), pp. 203, etc 

 t Records of the Geological Survery of India, Vol. XXII, Part I, pp. 51, etc- 



