84 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The lowest two beds of this section, below the yellow clay seam, are 
Eocene Tertiary, and similar to the beds exposed on Rio Formoso, south 
of the Guadalupe church. The beds above the clay seam rest uncon- 
formably against the early Tertiary as shown on p. 30. 
The sandstone reef of Rio Formoso (not including here the southern 
end buried by the sands and to be spoken of further on) begins on the 
southwestern side of the river or estuary on the Praia dos Carneiros, and 
extends northeast in an almost straight line across the mouth of this 
stream, and at right angles to it." 
The northern end of the reef curves westward slightly but distinctly ; 
this curve, however, is not apparent on the small-scale map given 
herewith. 
On an average, the reef is twelve metres in width, and stands a little 
more than one metre above water at ordinary low tides. Its entire 
length is two thousand and seventy metres. Its general appearance 
varies somewhat with the locality: near the south shore, to which it is 
Fico. 52. Profile of the etched sandstone reef at Rio Formoso. 
united, it is broad and flat, and comparatively smooth. Structurally 
this reef has a slight but very apparent seaward dip. In surface 
contour, the outer or oceanward side generally slopes at an easy angle 
along the whole length of the reef, and as it dips beneath the water 
becomes covered by corals and other marine animals and plants and 
their skeletal remains. In many places the top is covered by rough 
jagged points left by the wearing or etching away of the softer or more 
soluble surrounding parts of the rock. These points are a third of a 
metre or less in height, and often so close together and so sharp as to 
make walking through or over them almost impossible. They are 
extremely hard, and can be broken only by a sharp blow with a heavy 
hammer. When struck, the larger ones ring with a clear metallic 
up from the seaward side, and heaped upon the original bed, until they are from 
five to seven metres thick, and three or four hundred metres wide. If there should 
be any demand for such materials in this part of Brazil, a short tramway along 
the front of these beds could deliver the sands on board of barcagas at the foot of 
the Guadalupe hill. 
1 Liais speaks of a triple line of reefs at Rio Formoso. (L’Hspace Celeste, 549.) 
There are no such reefs at this place unless one considers the patches of coral 
outside the stone reef as such. 
