024 NEW SOUTH WALES. 
vails over large areas, and is nearly constant in dip; in the cliff of the 
South Head of Port Jackson, very many of the layers show more or less 
of it. The frequent changes in a single layer to a horizontal structure, 
indicate the variations in the force of the waves, and possibly variations 
in the state of the tides. When a part of a layer consists of oblique 
lamine of deposition, and the other part of horizontal, it is generally 
the lower part which is characterized by the oblique depositions; as if 
these were produced by a heavier sea, and the horizontal when the 
sea subsided; and we may almost fancy that the results are in some 
instances the effect of a single tide, or perhaps more probably of a 
single storm in the ocean of the period. We had occasion to observe 
this variation in a striking manner at the mouth of the Columbia 
River. During the rise or fall of the tide, the sea on the bar was so 
heavy that the boats were unable to pass from the ship Peacock, then 
aground ; breakers six or eight feet in height rolled in successively 
with great violence, though the weather was calm. But at ebb tide, 
the surface was nearly smooth and the boats pulled back and forth, 
landing the crew from the wreck. In a few hours the tide had set in 
strongly again, and so heavy were the seas, that the boats attempted 
in vain to reach the vessel for the rernainder of those aboard, and one 
with its crew was near being lost. ‘They were compelled to wait for 
another ebb tide. In periods of gales the waves are still more violent. 
It is obvious that the action here explained will account for the 
variations in the stratification in New Holland. Of similar character 
is the action of the swell of the sea upon the bottom in the shallow 
waters of a coast, especially when there are extensive flats washed 
over by the sea. It has been shown by M. Siau that the agitations 
of the sea even at great depths produce parallel ridges or ripples on 
the bottom.* 
It is important to observe that off the east coast of New Holland 
there is now acurrent analogous to the Gulf Stream, flowing from the 
northeast, and thus corresponding actually with the direction here 
demanded to account for the dip of the inclined layers of deposition. 
This current would have washed over New Holland in the same 
direction were the country at any time submerged, and from that 
direction would the waves travel onward across the accumulating 
sands. ‘The granite summits or ridges, many greenstones or basaltic 
peaks, and the limestones and older slates in or beyond the Dividing 
range, may have been in part the land of the period. The twelve or 
fifteen hundred feet of sandstone in New South Wales must have 
* See farther, page 105. 
