488 NEW SOUTH WALES. 
subdivides, but to the westward it continues for several rods. Some 
other peculiarities might be remarked upon, but we refer to the figure 
for a knowledge of them. 
The walls bordering a fissure between concretions have mostly a 
reddish or ferruginous aspect, while the areas they enclose are gray- 
ish-blue. It was somewhat surprising, after finding the fact just 
stated very generally true, to discover that in a few places where the 
rock was a little reddish, the walls, for an inch each side of the fis- 
sure, were a light grayish-blue like the ordinary sandstone,—yjust the 
reverse of the previous statement. 
These fissures or cracks are various in their directions. They cross 
at all angles, and often abut against one another without crossing. 
The concentric structure passes into the globular, and occurs where 
there are no cracks or fissures. Around Wollongong Point, the wide 
platform of rock, lying at high water mark along the shores, presents 
singular examples of these globular concretions. ‘They appear as if 
large cannon-balls had been dropped into a bed of mud, and sunk, 
some half their diameter, others three-fourths or more; and _ subse- 
quently the mud had hardened around them. The water, by removing 
the softer portions of the layers, has left the spherical balls projecting 
generally a hemisphere above the surface. More regular spheres than 
many of them could hardly be formed by art. The average size is 
about four inches; but they occur from an inch, and even smaller, to 
a foot in diameter. ‘They are extremely compact and hard, requiring 
smart and repeated blows to break them, while the adjoining rock 
yields with little difficulty; a few blows will readily detach them 
from the rock, in which they lie like foreign masses. 
These natural cannon-balls generally contain some foreign body, 
and in one-third of them, at least, it is a fossil; in this case they 
easily split in the direction of the fossil. In some there is a fragment 
of carbonized wood or a pebble. In many no nucleus could be de- 
tected; and often the foreign body, when present, was far from the 
centre. ‘The texture generally is equally hard throughout, though 
occasionally having the centre soft. Along the shores they may be 
sometimes found hollow, with a single small hole by which the water 
entered and gradually hollowed them out. . 
These concretions are mostly confined to particular layers. Some 
of the layers in the cliff near the extremity of Wollongong Point 
appear to be wholly composed of flattened globular masses, united 
laterally into a continuous bed of large extent: and this structure 
