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Geological Society of London. 
of moderate thickness, elevations such as suggested in the Address might well suffice 
to bring about a shifting of the crust, either by sliding on the fluid or viscous interior, 
or by causing it to undergo a certain amount of gradual deformation. The thinner the 
crust, provided it were sufficiently rigid to support the elevations once made upon it, 
the more readily would its geographical position be changed with regard to the poles. 
With regard to the thickness of the crust at the present time, he did not despair of 
astronomers at last conceding a less thickness than that assigned by the late Mr. 
Hopkins and Sir William Thomson. He was glad to find that the latter, in his 
Address to the Mathematical Section of the British Association at Glasgow, was 
willing not merely to admit, but to assert as highly probable, that the axis of 
maximum inertia of the earth and the axis of rotation, always very near one another, 
may have been in ancient times very far from their present geographical position, and 
may have gradually shifted through 10, 20, 30, 40, or more degrees, without at any 
time any perceptible sudden disturbanee of either land or water. 
Mr. George Darwin, also no mean mathematician, in his paper recently communi- 
cated to the Royal Society, agrees as to the probability of large geological changes 
affecting the position of the poles, and regards the effect of such changes as possibly 
cumulative. 
Mr. Evans feit that the Society was much indebted to Mr. Twisden for having 
likewise investigated the question, in which, of course, he was personally much 
interested. 
Prof. Ramsay referred to the former prevalence in Geology of views which had 
long since been exploded, and expressed his opinion that before long the theory of 
the fixed geographical position of the poles of the earth would share the same fate, 
and that the position of the poles would be regarded as very variable indeed. The 
Flora of various deposits in Polar lands indicated the growth of plants which would 
require the Stimulus of light, even if the necessary amount of heat for their growth 
could be aecounted for. With respect to great local changes of level, he remarked 
that the northern part of Africa was 4000 feet below the level of the sea in very 
recent times, and there was considerable reason to suppose that even later than the 
Miocene a vast tract of land occupied the space between what were now the con- 
tinents of Africa and India. Of course no one supposed that the position of the 
poles had been changed by rapid uplieavals of land ; but as we know that all geo- 
logical changes of level have been slow and gradual, so the poles may have altered 
their position by a process as slow as that of evolution which has originated the 
species of aniraals and plants during the long series of geological time. Such 
questions as these were serious questions involving the results of much observation, 
and could not, he thought, be solved in the closet by any amount of geological work. 
Prof. T. McKenny Hughes, Mr. A. W. Waters, the Rev. J. F. Blake, and Prof. 
Seeley, also took part in the discussion, and the author briefly replied. 
2. “ Note on a Specimen of Liploxylon, from the Coal-formation of Nova Scotia.” 
By J. W. Dawson, LL.D., F.R.S., F.G.S. 
The author described the occurrence in Coal-measure sandstone at the South 
Joggins of an erect stump of a Sigillarian tree 12 feet in length. It originated 
in a coaly searn 6 inches thick, and terrainated below in spreading roots ; below the 
coal-seam was an under-clay 3 feet 4 inches thick, separating it from an underlying 
seam of coarse coal. The stem, which tapered from about 2| feet in diameter near 
the base to 1J foot at the broken end, was a sandstone cast, and exhibited an internal 
axis about 2 inches in diameter, consisting of a central pith cylinder, replaced by 
sandstone, about § inch in diameter, and of two concentric coats of scalariform tissue, 
the inner one inch in thickness, the outer constituting the remainder of the axis. 
The scalariform tissue of the latter was radially arranged, with the individual cells 
quadrangular in cross section. A few small radiating spaces partially filled with 
pyrites obscurely represented the medullary rays, which were but feebly developed ; 
the radiating bundles, passing to the leaves, ran nearly horizontally, but their structure 
was very imperfectly preserved. The cross section, when weathered, showed about 
twenty concentric rings ; but these under the microscope appeared rather to be bands 
of compressed tissue than true lines of growth. The thick inner bark was replaced 
by sandstone, and the outer bark represented by structureless coal. On a small 
portion of one of the roots the author traced the remains of stigmarioid markings. 
From the above characters the author identitied this tree with Liploxylon of Corda, 
and stated that it was the first well-characterized example of this type of Sigillarians 
