branner: the stone reefs of brazil. 39 



In contrast with the outer face there are but few big blocks along the 

 inner face of the reef, and these are but slightly removed from their 

 original positions. The depth of the water close to the reef along much 

 of its inner face shows it to be a steep-faced wall, in places five metres 

 or more in height. 



To the landward of this main reef are to be seen here and there, 

 especially at low water, portions of an inner, subordinate, and somewhat 

 lower stone reef. This inner reef is approximately parallel with the 

 outer one, in some places uniting with it, in others di'awing away from 

 it. The rock of this subordinate reef is the same as that of the larger 

 reef, but as a rule not so hard. From a point fifty-five metres south of 

 the fort this inner reef runs southward parallel with the outer one, and 

 from eighty to ninety-five metres away from it, for a distance of a kilo- 

 metre. As compared with the main reef, this one is rather narrow, 

 being only from nine to thirty-five metres wide. Along this southern 

 end the inner reef is so low that it is all covered by ordinary high tides. 



Fig. 15. Section across the stone reef. Natal. 



At the fort the outer and inner reefs unite, and it is on the broad part 

 formed by this junction that the fort is built. North of the fort again 

 the two reefs no longer appear as one. The inner reef here apparently 

 comes to an end, and the only remnant of it visible is on the northern 

 side of the river and opposite the bar, where it forms a breaker uncovered 

 at low tide. 



Much of the surface of the whole reef is so covered with Algae, coral- 

 lines, barnacles, and polyps that the nature of the rock is not apparent. 

 In some places again the rock is bare, and large sand grains, pebbles, and 

 shells may be seen protruding on the surface. Everywhere the freshly 

 broken rock shows it to be a hard sandstone, so hard in fact that the 

 quartz grains and pebbles often break squarely across, and the fresh 

 fracture glistens very like that of a quartzite. Loose slabs and project- 

 ing points of the rock often ring under the hammer like clinkstone. 



One of the most striking characteristics of this rock is the fresh 

 appearance of the fossil shells it contains in abundance. These shells 

 are apparently the same as those found living upon the adjacent beaches 

 and sandbars. 



