BRANNER: THE STONE REEFS OF BRAZIL. 108 | 
| In the south end of the village of Sáo Thomé and just south of the 
hill on which the church stands (Е on the map) a gully has been washed | 
out in ап 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 Thomé 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 (Н on map), is a small stream called the Tubarão. 
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 
4 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. 
Periperí on the Bahia railway stands in a semicircular, flat-bottomed | 
valley very like that at São Thomé, and the sands of its floor contain an 
abundance of marine shells. Ido not know the elevation of this valley || 
| floor, but it is low — not exceeding three or four metres. 
| Marine terrace at Ilheos, Bahia. — The evidence at IIheos consists of 
| terraces. One of these —the Opába 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- 
1 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. $, Geological Survey, and found to be a good typical diabase composed | 
of basic feldspar, monoclinic pyroxene, and magnetite. 
