At S. Nicolas, M. d'Orbigny found remains of a Canis, Ctenomys, and Kerodon; and M. Isabelle ("Voyage" page 332) refers to a gigantic Armadillo found there. At S. Carlos, I heard of great bones. A little below the mouth of the Carcarana, the two skeletons of Mastodon were found; on the banks of this river, near S. Miguel, I found teeth of the Mastodon and Toxodon; and "Falkner" (page 55) describes the osseous armour of some great animal; I heard of many other bones in this neighbourhood. I have seen, I may add, in the possession of Mr. Caldcleugh, the tooth of a Mastodon Andium, said to have been found in Paraguay; I may here also refer to a statement in this gentleman's travels (volume 1 page 48), of a great skeleton having been found in the province of Bolivia in Brazil, on the R. de las Contas. The furthest point westward in the Pampas, at which I have HEARD of fossil bones, was high up on the banks of R. Quinto.
In Entre Rios, besides the remains of the Mastodon, Toxodon, Equus, and a great Dasypoid quadruped near St. Fe Bajada, I received an account of bones having been found a little S.E. of P. Gorda (on the Parana), and of an entire skeleton at Matanzas, on the Arroyo del Animal.
In Banda Oriental, besides the remains of the Toxodon, Mylodon, and two skeletons of great animals with osseous armour (distinct from that of the Glyptodon), found on the Arroyos Sarandis and Berquelo, M. Isabelle ("Voyage" page 322) says, many bones have been found near the R. Negro, and on the R. Arapey, an affluent of the Paraguay, in latitude 30 degrees 40 minutes south. I heard of bones near the source of the A. Vivoras. I saw the remains of a Dasypoid quadruped from the Arroyo Seco, close to M. Video; and M. d'Orbigny refers ("Voyage" Geolog. page 24), to another found on the Pedernal, an affluent of the St. Lucia; and Signor Angelis, in a letter, states that a third skeleton of this family has been found, near Canelones. I saw a tooth of the Mastodon from Talas, another affluent of the St. Lucia. The most eastern point at which I heard of great bones having been found, was at Solis Grande, between M. Video and Maldonado.
CHAPTER V. ON THE OLDER TERTIARY FORMATIONS OF PATAGONIA AND CHILE.
Rio Negro. S. Josef. Port Desire, white pumiceous mudstone with Infusoria. Port S. Julian. Santa Cruz, basaltic lava of. P. Gallegos. Eastern Tierra del Fuego; leaves of extinct beech-trees. Summary on the Patagonian tertiary formations. Tertiary formations of the Western Coast. Chonos and Chiloe groups, volcanic rocks of. Concepcion. Navidad. Coquimbo. Summary. Age of the tertiary formations. Lines of elevation. Silicified wood. Comparative ranges of the extinct and living mollusca on the West Coast of S. America. Climate of the tertiary period. On the causes of the absence of recent conchiferous deposits on the coast of S. America. On the contemporaneous deposition and preservation of sedimentary formations.
RIO NEGRO.
I can add little to the details given by M. d'Orbigny on the sandstone formation of this district. ("Voyage" Part Geolog. pages 57-65.) The cliffs to the south of the river are about two hundred feet in height, and are composed of sandstone of various tints and degrees of hardness. One layer, which thinned out at both ends, consisted of earthy matter, of a pale reddish colour, with some gypsum, and very like (I speak after comparison of the specimens brought home) Pampean mud: above this was a layer of compact marly rock with dendritic manganese. Many blocks of a conglomerate of pumice-pebbles embedded in hard sandstone were strewed at the foot of the cliff, and had evidently fallen from above. A few miles N.E. of the town, I found, low down in the sandstone, a bed, a few inches in thickness, of a white, friable, harsh-feeling sediment, which adheres to the tongue, is of easy fusibility, and of little specific gravity; examined under the microscope, it is seen to be pumiceous tuff, formed of broken transparent crystals. In the cliffs south of the river, there is, also, a thin layer of nearly similar nature, but finer grained, and not so white; it might easily have been mistaken for a calcareous tuff, but it contains no lime: this substance precisely resembles a most widely extended and thick formation in Southern Patagonia, hereafter to be described, and which is remarkable for being partially formed of infusoria.