TRANSACTIONS OF SECTION C. eves 
cussion we must not forget the transference of large portions of the earth’s crust 
from one region to another. Fifteen thousand feet of rocky material taken off a 
continent and thrown down on its margin must produce an appreciable disturb- 
ance, as we see on a small scale when a solid stratum is remoyed from above a 
shale or a mountain side, in a tunnel or in a quarry. The removal of blankets 
of sediment from one area and the heaping on of corresponding layers elsewhere 
must affect the transmission of heat and its many consequences. We must 
remember the different volume of rocks in a molten and solid state, and the 
tremendous power of crystallisation and chemical reacticns. We must be careful 
not to think that we can explain the working of a clock when we have given a 
numerical estimate of the strength of the spring, without taking account of the 
controlling influence of the pendulum, 
Professor Sotias remarked that Mr. Horne in his closing words had suggested 
the question which was most open to discussion, 7.e., How far could the hypothesis 
of a cooling globe be shown to explain the phenomena of disturbance in the super- 
ficial structure of the earth’s crust? It was difficult to enter upon this inquiry 
without making some assumption as to the internal state and constitution of our 
planet. Professor Arrhenius regarded the interior as consisting of gas at a 
temperature above its critical point, but under a pressure which rendered it highly 
incompressible. Such a conception would afford the geologist a general contrac- 
tion sufficient to meet all his needs. The Rev. O, Fisher, as the result of his 
investigations, had been led to regard the interior as fluid, but thought that even 
so the contraction resulting from cooling would be inadequate to account for the 
inequalities of the surface. While Mr. Davison, reasoning from Lord Kelvin’s 
hypothesis of a solid earth, was led to an opposite result. But however authori- 
ties might differ as to the amount, none would deny that some contraction would 
follow trom the secular cooling of the globe, and it was of interest to inquire by 
what kind of machinery this would act to produce mountain folds, with their 
associated thrust-planes and volcanic and seismic disturbances. It must be care- 
fully borne in mind that folding is confined to comparatively narrow belts of the 
earth’s surface, extensive masses of sediment remaining comparatively undisturbed 
in approximately horizontal platforms ; that these belts occur near the margin, or 
the once existent margin, of the ocean, and that they are comparatively super- 
ficial, the causes which gave rise to them being deeper seated. If we consider the 
relative level of the continents and ocean-floor, we find the latter lies at an average 
depth of some two miles below the former, yet the continents appeared to be self- 
supporting. Wherever great folded ranges are in existence, however, we have 
evidence of a previous slow subsidence of the sea-floor bordering the land, a sub- 
sidence which, with lapse of time, had in many cases amounted to five or six 
miles. When the present difference in level between continent and ocean-floor 
had undergone so great an increase as this, it was doubtful whether the continent 
would continue to sustain itself, and if it gave way it would slide towards the 
ecean. Consideration of the distribution of pressure and isogeotherms below the 
crust suggested the possible existence of a zone of solid material near its critical 
fusion point, the slope of which might be seawards, and might lead to the formation 
of gently inclined glide planes. The movement of the continental mass would 
then give rise to compression, folding, and overthrusting of the marginal sediments, 
as well as accompanying seismic and volcanic action. The limited distribution of 
folded belts could be thus accounted for; but it might still be urged that the 
contraction due to cooling was inadequate to explain the subsidence on which this 
theory was based. There was, however, another cause to which attention might 
be directed, viz., a slow deformation accompanying a loss of rotational velocity. 
Mr. Jeans had shown that the original form of the earth; subsequent to the origin 
of the moon, was probably pear-shaped, and this figure, of which some vestiges 
still remain, would determine the primitive distribution of land and sea. As 
rotational velocity diminished, the form would approximate more and more to that 
of an oblate spheroid, and the oblate spheroid would become more spherical; in the 
course of these changes the Pacific belt of continents would be produced, and the 
