THE HAWKESBURY SANDSTONE, 69 
on these islands has become converted into a calcareous sandstone, 
in which both marine and land shells are embedded. These islands 
abound with Helix Fosteriana, Pfr., which is a good-sized but very 
light shell. It is to be remarked that though the sand on these 
islands is white yet the rocks derived from them are of a deep brown 
colour, which is the case with all rocks derived from coral that I 
ve seen. It is also the case with calcareous aerial rocks generally. 
Lamination.—It occurred tome that the cause of lamination might 
be explained by experiment. I had noticed, in watching the accu- 
mulation of heaps of sand in an hour-glass or in a common egg-boiler, 
that the sand formed a narrow pyramid on which the lighter 
particles gathered for a time into a little pinnacle of sand and then 
suddenly slipped down ; thus the grains became distributed by a 
series of sandslips. Perhaps then a record of these slips could be 
preserved by using different-coloured sand. For this p I 
stained a quantity of fine sand with two or three different dyes. 
Using a very fine pipette glass fixed to a stand, I let the sand fall 
through on to a board. As soon as a sand-slip occurred I changed 
the colour. When a considerable heap had accumulated, I damped 
centre and made a careful section with a piece of card. A beauti- 
ful series of laminations were exposed to view, the most of them 
having an angle of about 30° By covering the whole with red sand, 
ad then varying the experiment so as to draw the glass gradually 
along and give rise to sand-slips, first in one direction and then in 
wmother, a section was produced which gave a tolerably fair illus- 
tation of a layer with false bedding at opposite angles, or as we 
quently see, “herring-bone” lamination. 
Wet sand, of course, may lie at a much higher angle. In 
taking, the layers of clay and shingle are perfectly horizontal. 
is mode of deposition of deltas from fluvial or estuarine remains 
- iy ki must have deposited it in a different manner. 
Wren other hand, at as already stated, the late Sir 
gives an account of a formation at those islands 
