branner: the stone reefs of brazil. 153 



In the south end of the village of Silo Thome and just south of the 

 hill on which the church stands (F on the map) a gully has been washed 

 out in an old road that comes down at right angles to the beach. In 

 this gully the section as shown in Figure 45 is exposed. 



Twenty metres back from the beach the tops of these beds are about 

 2.1 metres above the highest tides. 



All over the two mangrove swamps shown on the map the crabs have 

 brought up from their burrows fragments of beach forms of mollusks — 

 shells of species that do not live in mangrove swamps. 



Before leaving Sao Thome it is worthy of note that the shells occur 

 on the beach in front of the village in an almost incredible abundance. 

 There is at this village a considerable industry in the manufacture of 

 lime, all of which is made of the shells raked up on the beach. 



Just north of Olaria station on the Bahia railway, and in the outskirts 

 of that village (H on map), is a small stream called the Tubarao. 

 Where this stream enters the bay, and on its north bank, there are 

 hardened beds of shells. They reach an elevation of a little more than 

 one metre above the highest tides. 



Some 300 or 400 metres south of Olaria station the Bahia railway 

 crosses a small bridge. About fifty metres east of the track at this 

 bridge the shell beds are a little more than one metre above high-tide 

 level. 



Periperi on the Bahia railway stands in a semicircular, flat-bottomed 

 valley very like that at Sao Thome, and the sands of its floor contain an 

 abundance of marine shells. I do not know the elevation of this valley 

 floor, but it is low — not exceeding three or four metres. 



Marine tentace at Ilheos, Bahia. — The evidence at Ilheos consists of 

 terraces. One of these — the Opaba terrace — is about a kilometre 

 north of Ilheos, and 300 metres back from the present beach. It lies 

 across the mouth of a small steep-sided valley of which a sketch-map is 

 given here (Fig. 86). 



The rocks of the hills on both sides of this valley are crystalline — 

 gneisses cut by dikes of diabase,^ and decayed to red clays at the sur- 

 face. Above the terrace is a marsh, and below it a shallow fresh-water 

 lake. The terrace itself is about 120 metres wide at the base, from 150 

 to 160 metres long, and 7.31 metres high. It has a steep front or down- 

 stream face — 40° and more — while the upper face slopes back very 

 gradually to the marsh. The material is all loose, light-brown, coarse 



1 One of these eruptives was kindly examined by Mr. H. W. Turner, late member 

 of the U. S. Geological Survey, and found to be a good typical diabase composed 

 of basic feldspar, monoclinic pyroxene, and magnetite. 



