. JULY 7, 1899. ] 
ultimately with the fundamental proposi- 
tion that dispersed meteoroidal matter 
might gather in slowly rather than precipi- 
tately. On this point hangs all the law and 
the prophets. 
If astronomers, physicists and mathe- 
maticians will jointly attack the forma- 
tional history of the solar system stage by 
stage, following each stage out into details 
of time and rate, and taking full cognizance 
of all the alternatives that arise at each 
stage, it will then be possible, perhaps, to 
decide whether the conditions of the early 
earth were such as to require a large or a 
small amount of heat from the sun for the 
sustenance of life,and whether the sun was 
wasting heat prodigally in those days or 
conserving it for later expenditure. The 
present measure of the earth’s needs may 
be no measure of its early needs. The 
sun’s present expenditure may be no meas- 
ure of its early expenditure. 
In view of all these considerations, I 
again beg to inquire whether there is at 
present a solid basis for any ‘sure assump- 
tion’ with reference to the earth’s early 
thermal conditions, either internal or ex- 
ternal, of such a determinate nature as to 
place any strict limitations upon the dura- 
tion of life. 
The latter part of the address is con- 
cerned with novel suggestions regarding 
the behavior of the supposed liquid surface 
of the earth in the stages just preceding its 
final solidification, involving a theory of the 
formation of the primitive surface rocks 
and of the original continents and ocean 
basins. The discussion of this I must leave 
to the petrologists, merely venturing the 
hint that they may find some occasion to 
reconstruct current petrological doctrines 
if they are to be brought into consonance 
‘with the new views offered. 
The point of greatest general interest in 
this part of the address is the sharp state- 
ment of opinion that, if the original lava 
SCIENCE. 17 
ocean had solidified equably in all its parts 
and produced a dead-level surface all 
around the globe, there seems no possi- 
bility that our present continents could 
have arisen to their present heights, or the 
ocean basins have sunk to their present 
depths, during twenty or twenty-five mill- 
ion years, or during any time however 
long. (Exact words previously quoted, p. 
897.) Lord Kelvin adds: ‘ Rejecting the 
extremely improbable hypothesis that the 
continents were built up of meteoric matter 
tossed from without, upon the already solidi- 
fied earth, we have no other possible alter- 
native than that they are due to hetero- 
geneousness in different parts of the liquid 
which constituted the earth before its solidi- 
fication’ (this JourNAL, p. 706). This is 
as strong an assertion of the necessity of 
assuming crustal and sub-crustal hetero- 
geneity as any advocate of a slow-accretion 
earth could wish. If the word ‘liquid’ 
and what follows be stricken out, and the 
words ‘meteoroidal aggregate’ be substi- 
tuted in the sentence quoted, it will be a 
rather too strong statement of the alterna- 
tive explanation which springs obviously 
from the meteorological hypothesis herein 
urged. It is not easy to see how such 
heterogeneity as is required to account for 
the continents and ocean basins could arise 
from a white-hot liquid-surfaced earth de- 
scended from a gaseous earth. To those 
who do not follow the petrological concep- 
tions of the address, but who conceive the 
hypothetical lava ocean to have been one 
great solution, stirred by convectional and 
other currents and depositing crystals as 
supersaturation arose from change of tem- 
perature or from change in the solution it- 
self, there seems not much more reason to 
suppose that its deposits would have been 
localized persistently on the sites of the 
present continents than to suppose that the 
present enveloping solution—the ocean— 
if duly concentrated, would localize in a 
