PROCEEDINGS OF GEOLOGICAL .SOCIETIES. 



33 



force along two parallel north, and south lines of eruption in this region, reach 

 ing through Chile, Bolivia, and Peru, for more than forty degrees of latitude. 

 These diorites, and more especially the rocks which they traverse, are metalli- 

 ferous ; and the author looks upon the greater part of the copper, silver, iron, 

 and other metallic veins of the countries as directly occasioned by the appear- 

 ance of this rock. 



Shales and argillaceous limestones, with clay-stones, porphyry- tuffs, and 

 porphyries form the mass of the Upper Oolite formation of Bolivia, equivalent 

 to Darwin's Cretaceo-Oolitic Series of Chile. At Cobija they are traversed in 

 all directions by metallic veins, chiefly copper, and which, as before mentioned, 

 appear to emanate from the diorite. 



Bed and variegated marls and sandstones, with gypsum, and cupriferous and 

 yellow sandstones, and conglomerates, come next in order; they have a thick- 

 ness of six thousand feet, and are much folded and dislocated. These are con- 

 sidered by the author to resemble closely the Permian rocks of Bussia. Fossil 

 wood is not uncommon in some of these strata, which extend for at least five 

 hundred miles north and south. 



Carboniferous strata occur chiefly as a small, contorted, basin-shaped series 

 of limestones, sandstones, and shales, with abundant characteristic fossils. 



The quartzites which are generally supposed to represent the Devonian 

 formation in Bolivia, but which the author is rather disposed to group as 

 Upper Silurian, are really not of very great thickness ; but are very much 

 folded, and perhaps are about five thousand feet thick. 



The Silurian rocks (perhaps fifteen thousand feet thick) are well developed 

 over an area of from eighty thousand to one hundred thousand miles of 

 mountain-country, including the highest mountains of South America, and 

 giving rise to the great rivers, Amazon, &c. These slates, shales, grauwackes, 

 and quartzites yield abundant fossils even up to the highest point reached, 

 twenty thousand feet. The problematical fossils known as Cntziana or Bilobites 

 occur not only in the lower beds, but (with many other fossils) in the higher 

 part of the series. 



Lastly, the differences between the sections made by M. D'Orbigny, M. 

 Pissis, and the author were pointed out, though for the most part difficult of 

 explanation. D'Orbigny makes the mountain Illemani to be granite ; it is slate 

 according to the author. M. Pissis describes as carboniferous the beds in 

 which Mr. Forbes found Silurian fossils, — and so on. 



" On a New Species of Macrauclienia (M. BoliviensisJ." By Prof. T. H. Hux- 

 ley, F.B.S., Sec. G.S, &c. 



Some bones, fully impregnated with metallic copper, which had been brought 

 up from the mines in Corocoro in Bolivia were submitted to Prof. Huxley for 

 examination. The mines referred to are situated on a great fault, and the 

 bones were probably part of a carcass that had fallen in from the surface, — the 

 copper-bearing water of the mines having mineralized them. A cervical and a 

 lumbar vertebra, an astragalus, a scapula, and a tibia show complete corres- 

 pondence in essential characters with those bones of the great Macrauclienia 

 Patachonica described by Prof. Owen in the Appendix to the "Yoyage of the 

 Beagle," but the relative size and proportions of the vertebra, the tibia, arid 

 the astragalus indicate a distinct species, much smaller and more slender ; and 

 in some points of structure this new form (M. Boliviensis) approaches more 

 nearly to the recent Auclienidce than to the larger and fossil species. The 

 fragments of the cranium show some peculiarities of form ; but, on the whole, 

 it has many resemblances to that of the Vicugna. 



Prof. Huxley pointed out that this slender and small-headed Macrauclienia 

 may have been the highland-contemporary of the larger M. 'Patachonica ; just 

 VOL. IV. E 



