The bark round the trunks must have been circularly furrowed with irregular lines, for the mudstone round them is thus plainly marked.

At a little distance inland, I obtained several sections of the bed E, which, though different in appearance from the lower bed F, belongs to the same formation: it consists of a highly ferruginous sandy mass, almost composed, like the lowest bed at Port S. Julian, of fragments of Balanidae; it includes some pebbles, and layers of yellowish-brown mudstone. The embedded shells consist of:

I may add that specimens of this white mudstone, with the same identical characters were brought me from two points, one twenty miles north of S. Julian, where a wide gravel-capped plain, 350 feet in height, is thus composed; and the other forty miles south of S. Julian, where, on the old charts, the cliffs are marked as "Chalk Hills."

Above this fossiliferous mass, there is a stratum of very fine-grained, pale brown mudstone, including numerous laminae of selenite. All the strata appear horizontal, but when followed by the eye for a long distance, they are seen to have a small easterly dip. On the surface we have the porphyritic gravel, and on it sand with recent shells.

AA. Superficial bed of reddish earth, with the remains of the Macrauchenia, and with recent sea-shells on the surface. B. Gravel of porphyritic rocks. C. and D. Pumiceous mudstone. Ancient tertiary formation. E. and F. Sandstone and argillaceous beds. This case, though not coming strictly under the Pampean formation, may be conveniently given here.

Bed 10, a thick bed of rather bright green, indurated mudstone or tuff, with a concretionary nodular structure so strongly developed that the whole mass consists of balls. I will not attempt to estimate the thickness of the strata in the gypseous formation hitherto described, but it must certainly be very many hundred feet.

There are some thin beds of reddish mudstone, and soft ferruginous rotten-stones, with layers of gypsum. In nearly all these varieties, especially in the softer sandstones, there are numerous thin seams of rock-salt: I was informed that one layer has been found two inches in thickness.

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.

High up on this western flank, at a height estimated at 7,000 feet above the sea, in a broken escarpment of thin strata, composed of compact green gritstone passing into a fine mudstone, and alternating with layers of coarser, brownish, very heavy mudstone, including broken crystals and particles of rock almost blended together, I counted the stumps of fifty-two trees.

At Port Famine much of the clay-slate is calcareous, and passes either into a mudstone or into grauwacke, including odd-shaped concretions of dark argillaceous limestone. Ancyloceras simplex, d'Orbigny "Pal Franc" Mount Tarn. 2. Natica, d'Orbigny "Pal Franc" Mount Tarn. 4. Pentacrimus, d'Orbigny "Pal Franc" Mount Tarn. 5. Lucina excentrica, G.B. Sowerby, Port Famine. 6.