74 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ward slope, rise about as high as the high tides, and have flat tops, — 
a topographic configuration in strong contrast with the rounded outlines 
of the granites. The reef sands originally sifted into the crevices in 
granites and hardened so as to enclose granite blocks here and there. 
The rock is a rather fine-grained quartz sandstone of a light brown color. 
It contains a few fossil shells. 
These fragmentary beach reefs and the Cape of Santo Agostinho itself 
are separated from the great stone reef by a gap or break four hundred 
metres wide and, according to the hydrographic chart, 44 fathoms deep. 
This gap is known as the Barra do Sudpe. It is the only break in the 
great reef through which barcagas can enter the bay and the rivers that 
flow into it. 
If the Suápe break were restored, the total length of the Cape Santo 
Agostinho reef from the cape to where it disappears beneath the sands 
Fra. 41. Section showing the relations of the stone reef and granite at Cape 
Santo Agostinho. 
north of the cape would be thirteen kilometres. How much of its 
southern end is buried beneath the beach sands we have no means of 
knowing. Even to-day, taking out the various gaps, we still have pre- 
served a reef something more than twelve kilometres in length. 
A striking feature of the Santo Agostinho reef is the long tide-pools on 
its surface and running lengthwise of it. Toward the northern end 
these pools are not so long or so deep, but toward the southern end there 
is one pool a metre deep and nearly three kilometres in length. In the 
photographs taken of the reef near Сала ба, the reef has the appearance 
of being double ; and in a sense it is double, for the pool is made by a 
softer series of beds that dips beneath the harder ones that form the 
reef's seaward face, and overlies another series of harder ones that forms 
the landward face. 
From end to end the reef is nearly straight; there is but one slight 
seaward bend opposite Camböa Point. The surface is for the most part 
