GEOLOGICAL CHANGES ON THE EAETH’S AXIS OE ROTATION. 
295 
great band from the Low Archipelago to the Caroline Islands, and embraces the greater 
number of the islands coloured dark-blue in his map. The boundary may be defined 
as passing through : — 
N. S. 
< ■> t A ^ 
Lat 3 | 5 | 15 | 22 | 18 | 10 | 5 | 5 | 15 | 25 | 30 | 18 | 15 | 10 | 8 
Long 150 | 140 | 150 | 165 | 180 | 165 | 150 | 135 | 120 | 120 | 135 | 150 | 165 | 180 j 165 
v ) v* > E. 
E. W. 
He also marked a smaller area, embracing New Caledonia, the S.E. corner of New 
Guinea, and the N.E. coast of Australia. 
It is noteworthy that the former large area consists of sea more than 15,000 feet 
deep, except in patches round some of the islands, where it appears to be from 10,000 
to 15,000 feet deep*. 
I marked these areas on a globe, and cut out a number of pieces of paper to fit them, 
and then weighed them. By this method I determined that the former area was ‘055 
of the whole surface of the globe, and the latter was - 01 ; the two together were there- 
fore -065. 
It thus appears that we have some evidence of an area of between 5 and 7 per cent, 
of the globe having undergone a general motion of subsidence within a late geological 
period. But between this area and the coast of S. America there is a vast and deep 
ocean, and nothing whatever is known with respect to the movements of its bed. Hence 
it is quite possible that the area which has really sunk, in this quarter of the globe, is 
considerably larger than the one above spoken of. 
On the whole, then, perhaps from - 05 to T of the whole surface may at various times 
have partaken of a consentaneous movement, so as to convert deep sea into land, and 
vice versa. 
Besides this kind of general movement, there have certainly been many more or less 
local rises and falls, but this small oscillation is not fitted to produce any sensible effect 
on the position of the earth’s axis. 
18. Amount of Elevation, and the effects of Water. 
Humboldt has shown that the mean height of the present continents is a little less 
than 1100 feet from the sea-levelf. But this, of course, does not give the limit to the 
amount of change of level. On the other hand, there are perhaps 50,000 to 80,000 feet 
of superposed strata at most places on the earth ; but neither does this give the indi- 
cation required, because the surface must have risen and fallen many times during the 
deposition of these strata. 
But, as before pointed out, the actual upward or downward movement of land is by 
* See frontispiece-map to Wallace’s Geogr. Distrib. of Animals. 
f Sir J. Herschel seems to have doubled the height through a misconception of Humboldt’s meaning. 
The mean height of the land is in English feet : Europe, 671 ; N. America, 748 ; Asia, 1132 ; S. America, 1151. 
See a letter to ‘ Nature,’ by Mr. J. Garrick Moore, April 18th, 1872. 
2 T 
MDCCCLXXYII. 
