416 
Geology 7 
Newton computed it at 7, but I abide by Dr. Maskelyne 
and Mr. Cavendish, If, according to them, the whole 
mass of the earth be 5, the nucleus cannot be less than 6, 
considering the deductions to be made for the various earths 
forming the crust, the waters that cover so large a part 
of it, and the cavities that are most probably contained 
in it. 
Of what metallic substance ? Probably of iron and 
nickel : because these are the only magnetic metals ; and 
I know not how possibly to account for the phenomena 
of magnetism, but by means of a magnetic nucleus. 
Moreover, I cannot but suspect that some connection 
exists between the composition of meteorolites, all of 
which contain iron and nickel, and the subject of this in- 
vestigation. The specific gravity of metallic nickel is 
only 8.38, of iron 7.6 or 7.7. The nucleus however will 
more probably consist of the ores of these metals than the 
metals themselves : and we know that very many of the 
iron ores are magnetic and polar. These are conjec- 
tures : but the present state of our knowledge does not 
afford better. 
Are there any cavities intervening between the nucleus 
and the crust ? Cavities which admit of the entrance of 
atmospheric air ? 
It should appear that there are such. For, 
It is manifest that the whole series of formations from 
the uppermost alluvial soil down to the lowest granite, 
have in many instances been shaken en masse, from their 
foundations — upheaved. None of them are horizontal, 
as they were originally ; a fact tvhich Saussure first esta- 
blished : nor do any of them preserve an uniform dip or 
inclination. Marks of the revolutions they have under- 
gone ab imo, from the very deep, are not to be gainsaid. 
The lowest and deepest granite, is most generally found 
also as the outgoing, or as constituting the summit ofth£ 
