On the flexibility of itacolumite

O. A. Derby
1884 American Journal of Science  
HAVING had many occasions for observing the extensive series of quartzose rockf! known as itacolumite in t.he gold and diamond regions of Minas Gernes, Brazil, I have for some time entertained a suspicion that the peculiar property of flexibility would on investigation be fonnd to be only a surface character. I have already shown (this Journal, vol. xxvi, p. 34) that much of the so·called itacolumite belongs to a higher geological horizon than that containing the flexible layers and that in the
more » ... mountain of Itacolumi itself only a small part of the mass of the mountain is formed of the schistose beds of the lower series of quartzites in which alone, so far as I am aware, the property of flexibility has been observed. Even in the lower series flexible portions are rather uncommon, and the greater part of the mass is as rigid as any similar rocks. Artificial openings into this series of i'ocks are extremely rare, and so far itacolllmite has been studied in its natural outcrops only at the surface, in which it is generally impossible todetermine exactly how much the original characteristics of the rock have been modified by weathering. For some time past I have been on the lookont for an opportunity for studying unweathered itacohimite in order to determine whether ornot the flexible layers extend beyond the action of surface ag~ncies. Such an opportunity was recently afforded by the newly constructed Rio and Minas railroad. This line, starting * Quart. Journ. Gaol. Soc. Lond., xxxviii, 495.
doi:10.2475/ajs.s3-28.165.203 fatcat:e5bcatovqvgrtctfohqtcslkse