1889-90.] Mr Hugh R. Mill on Mean Level of Solid Earth. 187 
Using Dr Murray’s corrected figures,* we get — 
Area of lithosphere above contour-line of 1000 fathoms, 78,700,000 sq. miles 
,, below ,, ,, 118,200,000 ,, 
Or the ratio is 1 : 1 - 5. 
Area of lithosphere above contour-line of 2000 fathoms = 109,200,000 sq. miles 
,, below ,, ,, = 87,700,000 ,, 
Or a ratio of 1 : 0 *8. 
And by my experiment just cited — 
Area of lithosphere above contour-line of 1400 fathoms, 89,000,000 sq. miles 
,, below ,, ,, 107,600,000 ,, 
Or a ratio of 1 : 1 *2. 
As previously pointed out, recent researches show that mean- 
sphere level should he placed somewhat deeper than 1400 fathoms, 
and if this depth were 1700 fathoms the result would almost exactly 
correspond to an equalisation of areas. 
Pending the remeasurement of large-scale maps on which the 
results of the exploration of the Pacific at present in progress by 
British surveying ships can he represented, and pending also fuller 
knowledge of the relief of polar regions and of the gravitational 
distortion of the hydrosphere, it is imprudent to do more than point 
out the position of mean-sphere level as somewhere between 1400 
and 2000 fathoms beneath mean sea-level. At the same time it 
is to he noted that some contour-line between 1400 fathoms and 
2000 fathoms (probably that of 1700 fathoms) divides the surface 
of the lithosphere into two equal areas — one of elevation, one of 
depression. 
This coincidence can hardly he accidental, and although at 
present I do not see how the fact of the volume of the projecting 
portion of one half the lithosphere surface being equal to the volume 
of the depression occupying the other half hears upon physical 
geography and geology, the question demands, and will probably 
repay, investigation. If the substance of the globe were incom- 
pressible and elastic, it would follow that the depression of one half 
the surface would elevate over the other half a protuberance equal 
in volume to the depression. The depressed area is the region 
termed by Dr Murray the “ abysmal area,” and has distinct physical 
Scot. Geog. Mag., 1890, vol. v. p. 265. 
