OFF MOEETON BAT. 79 



Moreton, the reefs that stud the ocean around the New Caledonia 

 Group extend much nearer to the Australian coast than many 

 persons imagine, and betray the approach to the deep depression 

 just mentioned, the north-eastern edge of which seems to be 

 that of an uneven plateau or ridge in one spot, about 355 miles 

 from Cape Moreton, only 253 fathoms lower than the ocean bed 

 at a distance (on nearly the same bearing) of 36 miles from Cape 

 Moreton. The bottom of the depression is thus about 91 miles 

 wide, on each side of which there is an equal rise and fall of 

 about 41 feet to the mile, and this is about the mean general 

 steepness of the Blue Mountain Eange in New South Wales 

 along the railway line, from the summit to the waters of Port 

 Jackson. These calculations are not, of course, given by Captain 

 Miller ; but I submit them merely to illustrate the probable 

 slope of the coral reefs towards the west in the area referred to 

 and the contour of the depression. 



As the immediate coast of Queensland is comparatively low in 

 the part indicated, this great depression appears contradictory to 

 the usual idea of shoal water oiF a low coast ; but I would explain 

 it, as I do the condition of the sea bottom off the Illawarra coast, 

 as showing a double escarpment with an intervening compara- 

 tively level plain or plateau from the mountain summit to the 

 deepest sea bottom. One other inference is that our coast cur- 

 rent streams along from the north-eastward over this deep 

 depression and spreads its eddies under the impulse of winds. It 

 would be very interesting to be able to state the depth of water 

 in this current as well as the temperature below it from actual 

 experiments. Judging from what has been determined respecting 

 the Grulf Stream of the Atlantic, which is only 100 fathoms thick, 

 that off our own coast is probably still more superficial. Never- 

 theless it must have a powerful influence in modifying the climate 

 of the coast region, which is shown by the winter temperature of 

 the water in Port Jackson.* 



The depression in question is greater than that between our 

 southern line of coast and New Zealand, as determined by the 

 " Challenger." 



* During many years I have made comparative observations (but at 

 irregular intervals, and in various localities, on the ocean in the line of the 

 current) and have found the sea- water generally higher in temperature than 

 the air. I prefer, however, to quote here from a " Comparative table of 

 temperatures of sea-water and air" in Port Jackson, supplied at my request 

 by my excellent and accomplished colleague, H. C. Russell, Esq., Astron- 

 omer, from whose data, giving the temperatures for every month in the last 

 six years (1870-1875 inclusive) I collect that the mean for water is 65 "1, for 

 air 62*85 ; and that the maximum for water was 73*6, and for air 73*2 ; and 

 the minimum for water was 56"1, and for air 51 '2— all showing the influence 

 of the ocean water. 



