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PKOCEEDLNGS OF THE GEOLOGICAL SOCIETY. [Nov. 21, 



I was informed that a complete Saurian head had been extracted 

 from the same beds by M. Ramon Due, but was not successful in 

 obtaining it, nor some fossil bones and teeth now in the museum of 

 Avignon, in France, sent there by M. Granier, of La Paz. 



These beds are superposed quite unconformably on the Devonian 

 strata at Coniri (Section No. 2), where the red conglomerates, con- 

 sidered as the lowest beds of the series, abut against the nearly 

 vertical Devonian shales. 



The mineralogical characters of this system so strikingly remind 

 one of the descriptions of the Permian rocks of Russia by Murchison, 

 Keyserling, and De Yerneuil, that when reading it subsequently 

 to my arrival in England, it seemed as if treating of these very 

 strata. 



They consist of red, greenish, and variegated marls, saliferous and 

 gypseous marls, gypsum beds, along with fine red sandstones, thin 

 grey pebbly conglomerates, and red conglomerates. The marls are par- 

 ticularly well developed from Santiago to Nasacara (Section No. 2) : 

 at Laguna del Toro (Section No. 2) and at Corocoro (fig. 2, p. 41), 

 we have brownish-red sandstones, with indistinct vegetable impres- 

 sions, capped by thin gypsum beds and variegated marls. The 

 gypsum beds are frequently of great thickness and extent : in some 

 places, as at Berenguela, they are quarried to some extent, and pro- 

 duce abundance of fine alabaster, extensively used for the purposes 

 of architecture (for example, the fountain in the Alameda of La 

 Paz, &c.) : some of the slabs of this material are so transparent, 

 that tablets of it, until very lately, have been in general use in 

 this part of Bolivia as a substitute for window-glass : I noticed that 

 the windows of the church at Pisacoma were formed of this ma- 

 terial in slabs of about two inches thick. The sandstones vary from 

 red to brown in colour, and generally are not very compact, much re- 

 sembling occasionally the sandstones of this formation in England, as 

 at Pacheta (Section No. 2) we find them lighter in colour, and some- 

 times yellowish. The conglomerates, when intercalated with the sand- 

 stones, are generally of very insignificant thickness, often not many 

 inches across, and contain principally small rounded quartz-pebbles, 

 of the size of a nut, as at La Guardia (Section No. 1); those at 

 Coniri are of considerable thickness (probably some hundred feet), 

 and are of a deep red colour, and consist exclusively of rounded 

 fragments of quartzites, grauwackes, clay-slates, and granite, all 

 similar to those found in the eastern division of the diluvial forma- 

 tion before described, and evidently of the same origin. 



As in the European Permians, brine-springs are very common in 

 this formation ; and the cupriferous sandstones, here so well deve- 

 loped at Corocoro, Pisaca, San Bartolo, Santa Barbara, &c, appear 

 as the representatives of the similar cupriferous beds of Russia, the 

 Thiiringerwald and the Blarz ; and a further curious coincidence may 

 be found in the determination by Mr. Kroeber of the presence of 

 the rare element vanadium in the Corocoro copper-sandstones, — an 

 occurrence long known as peculiarly characteristic of the Thurin- 

 gian Kupfer-Schiefer. 



