BRANNER: THE STONE REEFS OF BRAZIL. 39 
Tn 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 drawing away from 
it. The rock of this subordinate reef is the same as that of the larger 
reef, but as а 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, 
Fre. 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, во 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, 
