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Brazil coast (32.(1))

Baron. Roussin. —¹

The coast N. of St Thomas (60 miles N. of C. Frio) is all low as compared to the part extending to St. Catherines
mention general soundings.

I have mentioned

Proceedings northwards from Bahia the coast is generally low. — I have mentioned shells in Limestone at R. S. Francisco. — At Alagoas. There is no hard rock, so that the ballast of ships is eagerly sought for. — At Pernambuco, the low sandy banks land on which the town is situated, is surrounded at a distance by a semicircle of hills, or rather by the edge of a bank country, elevated perhaps 200 ft above the sea: — I only had an opportunity of examining these at one place at Olinda. There a reddish cliff was composed of coarse par siliceous particles, very slightly aggregated, embedding. very numerous pebbles of white quartz. (a) —

(a) spotted with clayed matter

The mass might almost be called gravel. — Parts were glittering white, others red the colours being irregularly mottled; the super whole is horizontally stratified; the superior strata are redder & more aluminous. In the midst of the sand & pebbles: both layers & detached concretionary irregular masses of a quite white, or pale purple clay occur. — 3880:81 It is fine, soft & greasy to the touch, adheres to tongue, contains minute scales of mica & atoms of quartz. — The formation bore the

¹ Roussin 1826-7.

(a) spotted with clayed matter] added pencil.

1 verso

stamp of originating from the disintegration of granitic rocks. — At the base of these hills, & skirting the low swampy land, there are some fine grained yellow Limestone rocks. —

3877:78:79

These are very impure, being either sandy. aluminous or ferruginous; the stone is totally cor hard: it is associated with yellow clay: I could observe no embedded shells; but there are irregular cavities, which somewhat resemble the casts of vegetable matter. — I do not know whether these calcareous rocks pass under the sands & conglomerates, or merely face them. — I believe from what I heard, that the higher land in the neighbourhood, is all constituted of the granite sand such as that of Olinda. — There is an evident connection between this formation & the superficial one overlying the gneiss at Bahia. — I do not doubt. but to similar parent rocks occur likewise here, at some distance in the interior. —
North of Pernambuco, for the whole space

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N B. The remarkable facts respecting the reefs will be mentioned in the coral paper.

to the mouths of the Maranhao the coast is exceedingly low. — it is probable hard rock occurs in very few parts. — at C. Blanco, the cliffs are said by Roussin to be composed of white sand, which probably belongs to the same formation. — In the northern parts of this coast, there are extensive trails, desert & covered with dunes of white sand. —

Read Humboldt first volumes geology of Venezuela.¹

Near the mouth of Maranhao, clothed with green mangroves. —

Orbicular granite Daubuisson p. 308²

¹ Humboldt 1819-1829.

² Aubuisson de Voisins 1819.

Read Humboldt first volumes geology of Venezuela.] added pencil.