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Updated: June 16, 2025
On this there are two strata of the pale brown mudstone, also like that of S. Josef, separated by a darker-coloured, more argillaceous variety, including the Ostrea Patagonica. Professor Ehrenberg has examined this mudstone for me: he finds in it three already known microscopic organisms, enveloped in a fine-grained pumiceous tuff, which I shall have immediately to describe in detail.
At the head of the inner harbour of Port S. Julian, the fossiliferous mass is not displayed, and the sea-cliffs from the water's edge to a height of between one and two hundred feet are formed of the white pumiceous mudstone, which here includes innumerable, far-extended, sometimes horizontal, sometimes inclined or vertical laminae of transparent gypsum, often about an inch in thickness.
Turritella Patagonica, G.B. Sowerby. The fossiliferous strata, when not denuded, are conformably covered by a considerable thickness of the fine-grained pumiceous mudstone, divided into two masses: the lower half is very fine-grained, slightly unctuous, and so compact as to break with a semi-conchoidal fracture, though yielding to the nail; it includes laminae of selenite: the upper half precisely resembles the one layer at the Rio Negro, and with the exception of being whiter, the upper beds at San Josef and Nuevo Gulf.
Heard, reposing on the rough pumiceous ground with his eye fixed upon the naughty FLUTTERBY whose virginal whiteness, with declining day, had assumed a tell-tale crimson blush, pieced together these and sundry other little bits of information. They made him more than usually thoughtful; they chimed in with his momentary mood of self-analysis. One thing was dead certain.
For nearly a month after the eruption vast quantities of fine white ashes, mixed with volumes of steam, were thrown out from the crater; the clouds thus generated were condensed into heavy rain, and large tracts of the Vesuvian slopes were deluged with volcanic mud. It filled ravines, such as Fosso Grande, and concreted and hardened there into pumiceous tufa a very instructive phenomenon.
Salinas, or natural salt-lakes, occur in various formations on the eastern side of the continent, in the argillaceo-calcareous deposit of the Pampas, in the sandstone of the Rio Negro, where they are very numerous, in the pumiceous and other beds of the Patagonian tertiary formation, and in small primary districts in the midst of this latter formation.
The most eastern point at which I heard of great bones having been found, was at Solis Grande, between M. Video and Maldonado. 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.
These beds are covered by others of a peculiar soft white stone, including much gypsum, and resembling chalk, but really of a pumiceous nature. It is highly remarkable, from being composed, to at least one-tenth part of its bulk, of Infusoria: Professor Ehrenberg has already ascertained in it thirty oceanic forms.
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