516 Transactions. — Geology. 



soundings are separated from one another by water much less 

 deep, and the bottoms may not be connected. The distance 

 from the two extreme soundings is 450 miles. Specimens of 

 the bottom were recovered from the two deeper soundings, 

 and prove to be the usual red clay found in all the deepest 

 parts of the oceans. These soundings afford additional evi- 

 dence of the observed fact that the deepest holes are not in 

 the centres of the oceans, but are near land, as two of them 

 are within a hundred miles of the islands of the Kermadec 

 Group, and the other not far from a shoal. Doubtless deeper 

 depressions in the bed of the sea are yet to be found, but the 

 fact that this sounding of 30,920 ft. shows that the ocean con- 

 tains depressions below the surface greater than the elevation 

 of the highest known mountains is perhaps worthy of record." 



As to the question of heights and depths, a sounding has 

 recently been taken in the Pacific Ocean, near the coast of 

 Japan, which shows a depth of 29,400 ft., or approximately 

 five miles and a half. This is a little more than the heiglit 

 of the loftiest mountain — Mount Everest — which is situated 

 in the Himalayan Eange, to the north of India. It has been 

 suggested, as one theory of the formation of mountain-ranges, 

 that they represent the crumpling-up, or buckling, of the 

 earth's crust under the severe contraction strains that were 

 set up as the surface of the globe solidified. If this be ti-ue, 

 the deep ocean valleys or gorges, such as this ofi' the coast of 

 Japan, must be the result of the same action. Taken in con- 

 nection with the loftiest mountain, this sounding gives a 

 difference in distance from the earth's centre of about twelve 

 miles, or 1-333 of the earth's radius. 



On our way to Tonga we passed Pylstaart Island (22° 23' 

 south latitude, 176'^ 7' north longitude; height, 700ft. ; unin- 

 habited), which I certainly should consider to be formed by 

 volcanic upheaval. 



The visitor to Tonga cannot fail to be struck by the 

 numerous little islets standing upon the reefs at the different 

 entrances to Nukualofa and Vavau — their flat tops and steep 

 sides, and how the waves are undermining them and wasting 

 the solid coral away. He naturally concludes that these little 

 spots must have been upheaved from the sea, and that not 

 so very long ago, and by one and the same upheaval. 



On the 28th the steamer left Nukualofa for Hapaai (dis- 

 tance, 132 miles). On the way I noticed Tofoa, or Tofua 

 (1,890 ft.), and Kao, two grand huge dim-looking mountains 

 running up to 3,000 ft. I think Tofua is more constantly in 

 action than Kao (3,030ft.), which only emits puffs of steam 

 occasionally from its sides. Longitude, about 175° W. The 

 weather was too thick for us (after leaving Hapaai for Vavau) 

 to notice the smoke of the volcano on Tofua. (It was to that 



