. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 134 bulletin: museum of comparative zoology. metres wide, and is piled with dunes, some of them as much as ten metres high, but at and north of the village the rim is only about forty metres wide and two or three metres high. The land side of the lake is of Tertiary (]) sediments rising in a plateau from twenty to thirty metres high. A section from Sao Miguel church on these hills across the lake is given Fig. 71. Section from the hills at S. Miguel church across Lagoa Sinimbil. The history of the
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 134 bulletin: museum of comparative zoology. metres wide, and is piled with dunes, some of them as much as ten metres high, but at and north of the village the rim is only about forty metres wide and two or three metres high. The land side of the lake is of Tertiary (]) sediments rising in a plateau from twenty to thirty metres high. A section from Sao Miguel church on these hills across the lake is given Fig. 71. Section from the hills at S. Miguel church across Lagoa Sinimbil. The history of the place appears to be as follows : when the Tertiary sediments that form the coast plain rose from beneath the sea, they reached an elevation considerably higher than that at which they now stand. Erosion followed, cutting narrow valleys in these beds; then came a depression that carried beneath the sea the lowlands near the coast and the lower ends of some of the valleys. Marine erosion on the newly exposed beach-lines tore down the headlands, and the sands were heaped up by the waves as sand-bai's which, in time, separated the salt from the fresh water. The lakes along the coast of Ceara are produced, in my opinion, in one of two ways, either by the throwing up of beaches by wave action like those on the sandy west coast of France,^ or else by the shifting sands of the dunes damming back or changing the courses of rivers, as is known in Eio Grande do Norte, Ceara, and in Sergipe.^ One of the chief reasons for believing that certain lakes have been shut in by the constructive action of the present sea and not simply to have found ready-made basins is that if an opening be made in the rim separating the lake from the sea the breach is immediately closed by the sea. The lower courses of many of the rivers stand in the same relations to the sea as do lakes similarly located, except that the rivers are cer- tainly more capable of keeping tlieir mouths open than are lakes. Rios tapad
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Keywords: ., bookauthorha, bookcentury1800, bookdecade1860, booksubjectzoology
