SECTIONAL TRANSACTIONS.—E. 411 
may insist that geographers and geologists and climatologists do not simply ignore 
them, as Joly and Simpson have done. And astronomers may resent a geologist’s 
assumption that the earth captured the moon in Cretaceous times. Such people 
play fast and loose with every science but their own. 
The Rules of the Game are comprehended in the proposition : No man may adopt 
a principle contrary to the best opinion in another man’s subject. He should be 
encouraged to marshal evidence against the principles of others, but must give time 
for the defence and not anticipate the verdict. Mathematicians maintain firmly 
that any considerable wandering of the polar axis in the body of the earth is im- 
possible, and any considerable drift of the whole crust unlikely because there is no 
sufficient force to cause it. Differential drift of continents is even more difficult to 
allow. Geographers and geologists must, therefore, refrain from making contrary 
assumptions as a matter of convenience, and be content with accumulating evidence, 
carefully arranged in regard to the various mathematical objections. 
When the mathematician is able to allow enough thermal contraction to explain 
the Alps, the geologist is apt to demand immediately eight times as much to explain 
Central Asia, and to declare the contraction theory bankrupt because he cannot be 
allowed it. Thermal contraction must be allowed to play a large part in mountain 
building, and contraction with decrease of flattening something more. It remains 
to be seen if the two are insufficient. 
The theory of isostasy according to Bowie implies some uniform depth at which 
compensation is complete. Dutton originally used the word to denote conservation 
of the earth’s external figure against the processes of denudation and sedimentation. 
The doctrine of compensation at a definite depth is Pratt’s. Airy’s doctrine of the 
‘roots of the mountains’ is now definitely adopted by Jeffreys, and the basis of his 
mathematical reasoning. The word ‘isostasy’ is so closely bound up with the 
abandoned theory of Pratt that it should be dropped. Even the idea that the earth’s 
crust rapidly adjusts itself to compensation seems now to be doubtful from the 
discovery by Vening Meinesz of a belt of strong negative anomalies which coincides 
with the modern equivalent of Wallace’s line and is, therefore, a very old feature. 
AFTERNOON, 
Discussion of communications at Morning Session. 
Tuesday, September 29. 
Dr. 8. W. Wootpripcre.—The Geomorphology of the London Basin. 
The paper included a brief introductory survey of the evolution of the land- 
forms of the region, that is, its geomorphology strictly so called. Greater stress will 
be laid on the physical controls operative in water-supply, settlement and in the 
development of the conurbation of London itself. 
The London Basin is an asymmetrical syncline, pitching gently eastwards and 
drained by a longitudinal consequent stream and its tributaries. The major features 
of its present relief and structure bear a recognisable resemblance to those of earlier 
geological times, from which they may be regarded as inherited. The later (post- 
Miocene) stages of planation and dissection have followed a regular and orderly course 
which has imposed a definite scenic plan on the area. 
The London Basin is unique among the Tertiary basins of Europe in the number 
and variety of contrasted deposits which lie in geographically significant juxtaposition. 
Geographical contrasts are accordingly clearly marked, and regional subdivisions are 
readily made on a basis of soil-type and availability of water. Justification for the 
subdivisions proposed is found both in the history of post-Roman settlement and in 
the present utilisation of surface within the area. 
Mrs. H. Ormspy.—The Geographical Factor in the Growth of London as 
shown by Population Maps based on early and recent Census Figures. 
The population figures for the London area, as recorded in the report of the 1841 
census (the first systematic census carried out under the control of a central office), 
have been plotted, parish by parish and ward by ward, on the 6-inch map. The 
