PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
33 
force along two parallel north and soiitli 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. 
Red 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 Russia. Possil 
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 Soutli 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 Cruziana or Bilob/tes 
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 diificult of 
explanation. D'Orbigny makes the mountain lllemani to be granite ; it is slate 
according to the author. M. Pissis describes as carboniferous the beds in 
which Mr. Porbes found Silurian fossils, — and so on. 
" On a New Species of Macrmichenia (31. BoUviemis)P By Prof. T. II. Hux- 
ley, F.KS., Sec. G.S., &c. 
Some bones, fully imi)regnated with metallic copper, which had been l^rought 
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 sliow complete corres- 
pondence in essential characters with tliose bones of the great Maemnchenia 
Patachonica described by Prof. Owen in the Appendix to tiie "Voyage of tlie 
Beagle," but the relative size and proportions of the vertebra, the tibia, and 
the astragalus indicate a distinct species, much smaller and more slender ; and 
in some points of structure this new form (M. Boliviemh ) approaclies more 
nearly to the recent Aicchenida 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 Macrauchenia 
may have been the highland-contemporary of the larger M. 'Patachonica ; just 
VOL. IV. " E 
