62 NOTES ON DEEP SEA SOUNDINGS. 



of shallow water, which in the China Sea exceeds a breadth of 

 600 miles, and in the Celebes Sea is apparently about half the 

 length of the Macassar Strait." 



These and other collateral facts belonging to the arrangement 

 of the ocean bottom in basins of different depths, and separated 

 by ridges of various widths and extent may, I think, be con- 

 sidered to be in accordance with certain features of the present 

 surface of the earth. On a much smaller scale we have in 

 the Gold Fields oftheLachlan and Currajong a similar conforma- 

 tion, — hollows separated by ridges, in which drift has accumulated, 

 sometimes richly, sometimes poorly auriferous. Since the water 

 that occupies these basins in the Indian Ocean cannot get out to 

 mingle with the neighbouring waters at great depths, we have 

 only to consider that if instead of water the contents of the basins 

 were to be drift matter of various periods, and from various 

 sources, the very features of the gold field alluded to would be 

 explained, inasmuch as some of the deepest drifts have been found 

 of the least commercial importance. This observation will apply 

 to many other gold fields. 



There are some interesting data afforded by Commander 

 Tizard, relating to the changes of seasons affecting temperatures 

 of the ocean. At Manila, for instance, in 1870, the total evapo- 

 ration was 237 inches greater than the rainfall, but during the 

 first four months it was 28 inches greater than the rainfall, so 

 that there must have been an excess of 4 inches of rain over 

 evaporation during the remaining eight months. " In 1871 the 

 total evaporation was 32 5 inches greater than the rainfall, and 

 in the first four months 45 inches greater, leaving 12 5 inches in 

 excess of evaporation for the remainder of the year. The mean 

 rainfall at Manila is 95*36 inches." The average rainfall at 

 Labuan is 115 inches per annum, and only an average of 22 

 inches falls during the first four months of the year ; whilst at 

 Hongkong, where the total annual fall is 8014 inches, 7*77 

 inches only fall at the same period. 



Moreover, the winds affect the changes of temperature, for 

 during the N.E. monsoon the surface water is forced by the wind 

 into the China Sea from a higher and colder latitude, and in the 

 S.W. monsoon the surface water is forced out. 



In consequence of these changes and effects, and of the excess 

 of evaporation over the rainfall, " the surface water in the south- 

 west part of the sea becomes heavier and has a tendency to sink, 

 and in sinking carries with it its high temperature, which is 

 gradually imported to the deeper water of the sea. 



" The consequence of this is, that in the N.E. monsoon the 

 water in the China Sea has a tendency to sink and flow out at the 

 bottom into the Pacific Ocean, whilst in the N.W. monsoon it 



