Vice-President’s Address. 273 
may disregard the view I have referred to regarding the Age 
of the Earth. We may again advance, though most of my 
fellow-thinkers will agree with me in taking the lesson we 
have learned seriously to heart, so that when we do again 
advance, we may do so with much more cautious steps than 
many of us took before Lord Kelvin appeared at our head 
and gave us the order to countermarch. 
Relation of the Tertiary Rocks to those of the Cretaceous Age. 
—In the Mediterranean region, and in the adjoining parts of 
Asia, no line can be drawn between the limestones of Kocene 
age and those referred to the Cretaceous Period. But in 
Western Europe the difference between the Eocene fauna 
and that of the Chalk is generally regarded as so great as to 
imply that a long interval of time elapsed between the forma- 
tion of the two deposits. I shall endeavour to show that this 
difference is by no means as great as has been generally 
assumed. Moreover, an examination of almost every known 
section where the Lower Eocene Thanet Sands lie upon 
the Chalk, convinced me, over thirty years ago, that there 
is no trace whatever of any physical break between the 
two, or, at any rate, no more than might be expected to 
accompany a change of conditions from the warm surface- 
currents and the deep water of the Chalk sea to the colder 
surface-water and lesser depths of the sea in which the 
Thanet Sands were deposited. I therefore think it safer not 
to take into account, in the present connection, any interval 
of time which may possibly have elapsed between the close 
of the Chalk Period and the commencement of that during 
which the Eocene Thanet Sands were formed. The com- 
mencement of the period when the Nummulitic Limestone 
was formed immediately followed the close of the Cretaceous 
Period, and was not separated from this by any break. 
Time required for the Formation of the Chalk—The tiue 
measure of time required for the formation of the rock of any 
given geological period should be estimated with reference to 
the maximum thickness known to occur between an upper 
well-defined stage, characterised by life-zones whose contem- 
poraneity over a larger area has been well put to the test by 
many observers, and a lower stage equally well characterised 
