ORIGIN OF DEPOSITS. 519 
inches thick, and some rods in extent, occurring upon the layers of 
argillaceous sandstone, and also enveloped mwzthin them, and cracked 
or fissured as shown on page 480. These cracks are confined to the 
thin beds themselves, instead of extending into the rock above or 
below, and are precisely similar to what we often see over the bottom 
of shallow pools, after the water has evaporated. Moreover, the fine 
clayey material is just what settles in such places, and forms usually 
their bottom ; and besides, the ferruginous character is a common fea- 
ture of the waters of such pools, and consequently of the clay at 
bottom, after the evaporation of the water. We therefore ascertain 
not only the general fact that the land had emerged, but may point 
out also where there were spots of standing water, and read farther 
how they evaporated in the sun, and the fine mud of the bottom 
cracked on exposure. We also learn that the elevation of the emerged 
land was probably small; for, as stated, the remains of a fish were 
found in the lower coal deposit at Newcastle. From this last fact, 
we might think that the place was still beneath the sea; but not 
necessarily, for these animals are often thrown up dead on sea-shores, 
and floated over low flats by river floods; and the absence of other 
marine fossils, as well as the facts above stated, militate against the 
supposition. The logs and stumps of ancient Conifere, which are 
common in the lower portion of the coal series, call to mind the logs 
which are frequent in marshy lands, just emerging from the water ; 
and the clay-ironstone constituting these, resembles that of the thin 
ferruginous beds above described. ‘The waters of marshes often con- 
tain in solution the carbonate of iron, and also organic salts of this 
metal, while in broad streams of running water, such iron depositions 
do not take place. 
We infer, therefore, that the region where the coal strata of Aus- 
tralia were forming was an extended low flat, subject either to floods 
from fresh waters, or else connected with the sea and exposed to tidal 
inundations, besides the heavy waves that attend an earthquake or 
an elevation of the land. ‘The alluvial shores of our own southeastern 
coast, and that of Texas, are to the point as illustrations, affording 
examples of both the marine and fresh-water flats. Illawarra Lake in 
the district of Illawarra is a less perfect example, yet it is peculiarly 
interesting as showing the process of change from a salt-water to a 
fresh-water lagoon, owing to the simple action of the sea in accumu- 
lating beach sands; other portions of the same district have by this 
process been changed to dry land. 
