New-York tribune., 1900-10-07

is that Of Professor W. j. SOllas who occupies
the chair of geology at oxford, and is president
OF the geological section of the British Associa-
ton for the Advancement of Science This ad-
dress at the annual meeting of that organiza-
ton a fortnight or so ago, was devoted to re-
viewing the estimates of others and calculating
his own opinion on this interesting subject
It should be promised that inasmuch as matter
is believed to be indestructible the scientist has
difficulty in understanding how it could have
had beginning Hence, the material compos-
ing the earth is to be regarded as having ex-
listed forever, though it's condition may have
undergone many changes. However, even though
it may once have been a nebula, without form
and void" and though at one period in its his
tory It perhaps merged with the far greater
mass comprising the other planets and the sun,
there came time when it detached from
them all, acquired globular shape, and was
probably Though not certainly hot as to be
entirely molten 1t is customary, therefore, to
specify particular stage in its develop
ment as the starting point for calculations Of the
earths age Lord Kelvin, for instance, dated his
estimate from the time when the globe became
cool enough to be habitable by the lowest known
forms of life.
Kelvin placed the interval which has elapsed
since that era at between twenty and forty mill
ion years but he believed that it was nearer
the former figure than the latter. This com
putation was based principally on the rate at
which various kinds of rock will radiate heat.
and on the assumption that the rate has re-
mained uniform from temperatures like 2,OOO
and 800 down to that now observed at the
earth's surface Professor Sollas remarks, how
ever, that another factor in Kelvin's estimate
was the supposition that the temperature of the
earth increases one degree for every ffty-one
feet Of depth. whereas other authorities
80
believes that one degree for so or 90 feet would
be nearer the correct average He specifies sew
eral instances where it is even slower than this.
In the Lake Superior copper mines the rate is
one degree for every 223.7 feet of descent A
modification such as is here suggested would
bring Kelvin's figures up to about 5O,0O0OO0.
Then there is Professor George Darwin's
fascinating calculation based the belief that
the moon was thrown off from the earth in a
tidal wave. At that time the latter body was
supposed to be rotating on its axis in period
Of from two to four hours. The subsequent
retardation of its speed through the attraction
Of the moon would according to Professor Oar
wins mathematics. require something like fifty
six fifty-seven million years at least and
possibly more. Professor Sollas thinks that this
theory has strong claims to acceptance, and he
picks no flaws in it. though eventually offer
ing a different estimate of his own.
. Jolly based another computation on the sup
posed rate at which salt had been carried into
the ocean by rivers. But Professor Sollas Of
fers several reasons for suspectng that Jolly did
not adopt sufficiently rapid rate. He would
therefore cut down Joly's eighty ninety mill
ion year nearly one-half Indeed, Professor Sol
las courteously betrays a considerable lack OF
confidence in the ocean salt system of compu-
tation.
The particular class of evidence to which the
Oxford geOlOgst attaches the largest Importance
Is the depth of those rock formations which
are clearly of sedimentary origin Taking these
at their greatest thickness. wherever this may
occur, he finds an aggregate deposit Of about
80 miles, or 264,O0O feet. Great difficulty is
experienced in hitting upon an approximate ac-
curate average rate of deposition. But Professor
SOlas, after presenting elaborate reasons for so
doing, adopts one foot century the most
satisfactory standard; and with this basis he
gets little over 26,0O00OO years as the time
which has elapsed since the formation of sedI- !
mentary rocks began. The whole tendency of |
his argument is aVowedly to harmonic the esti-
mates Of others far possible, and it will
be observed that he comes much nearer to Lord
Kelvin's figures than to either Professor Dar-
wins or Professor Joly's.
Those who have followed the discussion of this
subject for more than quarter of a century will
recall that Huxley deemed a period of even a |
1OOOOOOOO years hardly adequate for the play
of forces whose activity is Self-recOrded In fha