. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 74 bulletin: museum of comparative zoology. ward slope, rise about as high as the ])igh 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 se
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. 74 bulletin: museum of comparative zoology. ward slope, rise about as high as the ])igh 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 hundi-ed metres wide and, according to the hydrographic chart, 4|^ 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 Su^pe break were restored, the total length of the Cape Santo Agostinho reef from the cape to where it disappears beneath the sands. Fig. 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 knoAving. Even to-day, taking out the various gaps, we still have pre- served a reef something more than twelve kilometres in length. A striking featuje 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 Camboa, 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 reefs seaward face, and overlies another series of harder ones that forms the landward face. From end to end
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