Lisboa — Pebbles on the Central Plateau of Brazil. 9 



Art. II. — The Occurrence of Facetted Pebbles on the Cen- 

 tral Plateau of Brazil ; by Miguel Arrojado R. Lisboa. 



After the observations that were made upon facetted peb- 

 bles — the German Dreikanter — by Koken and jNToetling in 

 the Salt Range of India, and by E. Philippi in the south polar 

 regions, the subject seems to be assuming the same importance 

 as when Behrendt in 1876 first brought it to the notice of the 

 Geological Society of Germany. 



A plausible explanation,* based on local observations, gave 

 rise to the theory of the glacial origin of the facetted pebbles 

 of the Salt Range. This theory became more plausible after 

 the discovery, by the Gauss expeditiou,f of facetted pebbles in 

 the Antarctic polar regions. 



The theory of glacial origin for all facetted pebbles is far 

 from being accepted by geologists, and several objections have 

 also been raised to the theory of their formation by the action 

 of wind-blown sand in arid regions. 



The occurrence of these pebbles in hitherto unknown locali- 

 ties will furnish a contribution to the subject worthy of atten- 

 tion. The author consequently takes the opportunity of 

 announcing the discovery of characteristic facetted pebbles on 

 the central plateau of Brazil. 



Only two references to the existence of facetted pebbles in 

 South America have been found. One of them, by Bracke- 

 busch,^: refers to their occurrence in the Argentine valleys near 

 the dunes derived from the sands of the Atacama desert, 4000 

 meters above sea level. In the valleys of Tinogasta and Belen, 

 effects analogous to those produced by glaciers were attributed 

 to the action of sand blown by winds over the Bolivian desert. 

 These facetted pebbles are, therefore, referred to as being of 

 seolian origin. The other reference in the journal of the Ger- 

 man Geological Society§ is a statement by Prof. Bruhns to the 

 effect that in the Strasburg collection of South American 

 rocks there are facetted pebbles of asoliau origin, but the 

 author does not know whether they come from the locality 

 mentioned by Brackebusch. 



When in 1884 Behrendt advanced the theory of the glacial 

 origin of Dreikanter, the occurrence of these pebbles was 



* E. Koken und F. Noetling, Geologische Mittkeilung aus der Salti'ange 

 (pandschab) Centralblatt fur Mineralogie, Geol. und Paleontology, 1903, n. 8, 

 p. 72, n. 4, p. 97. 



f E. Philippi, Ueber recente Facettengesehiebe von antarktische Eisbergen. 

 Centralblatt f. Min., Geol. u. Pal., 1904, n. 24, 737. 



% Petermann's Mittheilungen, 1893, xxxix, 153-158. 



§Zeitsckrift der Deutschen Geologiscben Gesellscbaft, lvi, Protokoll- 

 notiz, p. 1(58, 1904. 



