39 
30,000 years ?* With regard to the measurement of geological time, I am a 
u ^ Peri ° dS ° f time durin S whlch Hfe Has existed on 
,, , 1 /' Ut W ien we come to consider how many thousands or scores of 
housands of years man has existed, then I must admit fully that we are all 
m a haze. There is one point to which I should like to call attention with 
reference to the chronology of these gravel deposits, and that is the growth 
of the coral reefs. They have been made the subject of most efficient and 
caret ul study, and one of the most distinguished men living in the roll of 
those who have devoted their lives to scientific research— Mr. Dana, a pro- 
fessor in an American university -ascertained the depth of the coral reefs 
in the Pacific to be upwards of 2,000 feet. He finds the present rate of 
growth to be half an inch per year. Then he multiplies that half-inch by 
the measurement— and these, remember, are not geological reefs, but living 
reefs of the present day-and he finds they have taken 192,000 years for 
their growth I do not ask you to believe this, but men like Agassiz, and 
ye f, and Dana, and others, have exercised a great deal of intellectual 
power in order to arrive at solutions of questions of this kind, and have 
bestowed quite as much labour, of quite as high a class, as astronomers have 
upon their studies. There is this difference however between their 
chrono ogy, that when an astronomer tells us of bodies in the firmament 
w lose light has been thousands of years travelling through space before it 
has reached this earth, we feel bound to believe him, for he points out 
the exact date of an eclipse, and we find him right to a moment, f And when 
we see this, are we not justified in having faith in his calculations, 
when he comes before us with the marvellous and striking announcement, 
or, ’ni^' Thomson concluded, from different lines of argument, that the 
th ea i h aS a b ° dy C ° o1 enou S h for habitation cannot be much greater 
than 100 million years. Proiessor Tait, in his decent Advances in Phy- 
sical Science, recapitulates the same arguments, but with different conclusions 
1876)*— E^ 6 limit ° f age *° be ab ° Ut tm million years ( see Mature, April, 
t Astronomy, as a whole, is more certain than geology ; it is a more 
advanced science, and many parts of it depend on a definite law, already 
ascertained and involve fewer uncertain elements. But it by no means 
o ows that the more doubtful parts of astronomy are clearer and better 
. own than the plainest and simplest conclusions of geoloo-y. In all there 
Ml in ro n T DSe ^erval between the plainest parts and the most obscure. 
Mr Oharlesworth s remark must involve this assumption : Astronomers are 
“ c ® r “ m °f the distance of the most distant stars, or of the nebula of Orion, 
as of the relative distances of the sun, moon, and earth, on which the calcu- 
lation of eclipses depends ; but this is manifestly, and almost absurdly 
S rae - y ® see ^at they mistook nearly 4 millions of miles in the absolute 
distance of the sun till within the last few years. The notion of the immense 
distance of the nebula of Orion is one part or corollary of those views of 
the nebufie which recent observations have done so much to disprove. Mr. 
Proctors papers, for instance, all tend to establish quite a different view.”— 
(Communicated by Professor T. R. Birks, Carnb .) 
