President's Address. 27 
In the difference in the type of movement to which con- 
tinents and ocean-basins respectively owe their formation, 
we may, further, find an explanation of the fact that the 
ocean-floors are comparatively level, whereas the continents 
have been subjected to much fracturing and folding. This is 
readily intelligible on the view that the former are the result 
of the slow descent of larger or smaller parts of the earth’s 
crust as a whole towards the centre, whereas the latter have 
been mainly produced by crumpling of the crust. Hence 
this fact cannot be regarded as offering any special support 
to the doctrine of the “ permanence of the ocean-basins,” 
THE SIGNIFICANCE OF UNCONFORMITIES. 
Another argument which has been used in support of the 
doctrine in question is based upon the asserted “ remarkable 
parallelism and completeness of the series of geological 
formations in all the best known continents and continental 
islands, indicating that none of them have risen from the 
ocean-floor during any portion of known geological history, a 
conclusion enforced by the absence from any of them of that 
general deposit of oceanic ooze at some definite horizon, 
which would be at once the result and proof of any such 
tremendous episode in their past history” (Wallace, Natural 
Science, vol. 1., p. 425, 1894), It appears to me that the 
first portion of the above-quoted passage involves a proposi- 
tion conspicuously at variance with geological facts. So far 
from it being the case that the best known continents and 
continental islands exhibit a remarkable “completeness” of 
the series of geological formations, we know of no country in 
the world where we could find such a complete series. The 
“ geological record” is notoriously imperfect and incomplete. 
Everywhere we are confronted, at one horizon or another, 
with gaps in the series, marked by the existence of an uncon- 
formity. Some unconformities are quite local, but others are 
more or less general, and each indicates a period in which a 
pre-existing ocean-floor was elevated to form dry land, and 
in which no marine sediments were laid down in that 
particular region. With regard to the second portion of the 
