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NATURE 
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rejected by the reading of a proposition in a manner exactly 
answering to that in which a reasoning mind should treat its 
ideas, and at every step in the progress of a problem the machine 
indicates the proper condition of a mind exempt from mistake. 
It is believed that this logical machine may be usefully employed 
in the logical class-room to exhibit the complete analysis of any 
argument or logical problem ; and it is considered by the author 
superior for this purpose to a more rudimentary contrivance, the 
logical abacus, constructed by him for the same purpose. But 
by far the chief importance of the machine is in a theoretical 
point of view as demonstrating in the simplest and most evident 
manner the character and powers of a universal system of logical 
deduction, of which the first, although obscure solution, was 
given by Dr. Boole. 
“On Jacobi’s theorem respecting the relative equilibrium of 
a revolving ellipsoid of fluid; and on Ivory’s discussion of 
the theorem,” by I. Todhunter, F.R.S. Jacobi discovered the 
theorem that a fluid ellipsoid revolving with uniform angular 
velocity round its least axis might be in equilibrium. Ivory 
discussed the theorem, and made several statements regarding 
the limitations of the proportions of the axis. Ivory’s statements 
contain various errors, and truths based on erroneous reasoning. 
The object of the present memoir is to correct Ivory’s errors, to 
supply his imperfections, and to add something to what is already 
known respecting the theorem. 
Geological Society, January 12.—Professor Huxley, LL.D., 
F.R.S., president, in the chair, Messrs. J. Aitken, J.P., presi- 
dent of the Manchester Geological Society ; E. Allen, C. Cadle, 
A. W. Edgell, C. F. Leaf, F.L.S., and S. J. Smith, were 
elected Fellows. Prof. Otto Torell, of Lund, was elected a 
foreign correspondent. The following communications were 
read :—1.‘‘On the geological position and geological distribution 
of the reptilian or dolomitic conglomerate of the Bristol area.’’ 
By R. Etheridge, Esq., ¥.G.S., Palaeontologist to the Geological 
Survey of Great Britain. The author noticed the history of our 
knowledge of the dolomitic conglomerates of the Bristol area 
from which the remains of dinosaurian reptiles have been ob- 
tained, and then described their mode of occurrence and distri- 
bution over the district near Bristol. He regarded these deposits 
as due to the action of the sea-waves of the later or middle 
Triassic periods upon the rocks of older Triassic (Bunter) or 
Permian age during the gradual elevation of the land, 
and as the probable representatives in point of time of 
the Muschelkalk, otherwise deficient in Britain. The author 
then noticed the influence of the conglomerate upon the produc- 
tion of certain minerals, such as calamine and hzematitic iron- 
ores, and discussed at some length the probable course of the 
phenomena of denudation which furnished the materials for the 
formation of the conglomerate at different levels, in which he 
recognised two great periods of oscillation, the first witnessing a 
downward movement of the palzeozoic lands and lasting through- 
out the deposition of the New Red marl and sands, and the 
second, during which the accumulations of the former were 
again, at least partly, denuded. With regard to the time 
at which the remains of thecodont reptiles were imbedded 
in the conglomerate, the author inferred from the evidence 
that this took place late in the period of the Keuper. 
The President inquired on what ground the author considered 
these reptiles to belong to a late period in the Keuper, and was 
informed that the author spoke especially with relation to the 
Keuper of the Bristol area, of which the beds containing them 
occupied the highest position. Prof. Ramsay considered these 
conglomerates not merely as of marine origin, but as breccias 
which had covered the old land surface, which had been worked 
up by the water of the New Red period. He*objected to the 
term Sea having been introduced into the paper; as, though the 
tracts may have been islands and promontories, and though the 
water which surrounded them was salt, there was no open sea, 
but merely a large inland salt-lake, in which the New Red Marl 
was formed. ‘The marl was less connected with the New Red 
Sandstone than with the Lias. The Muschelkalk being absent, 
it was constantly the case that the marl rested immediately on the 
palzeozoic rocks without the intervention of the Bunter Sand- 
stone. He thought that there were good grounds for connecting 
the Rheetic beds withthe New Red Marl below and the Lias above. 
The probability was that the change in character was due toa 
gradual influx of the sea into the inland lakes. He thought that 
the Thecodont Saurians might also eventually be found even in 
beds of Liassic age. Prof. T. Rupert Jones remarked that 
Mr. Tawney and Dr. Duncan had already intimated the St. 
Cassian aspect and character of the Sutton beds. The freshwater 
character of some of the Keuper beds was, he remarked, indicated 
by the presence of Zstherie, and he alluded to the fact of the 
Bristol palzeosaurians having been erroneously used as Permian 
characteristics in Russia and Carolina. Mr. W. Boyd Dawkins 
had found at Cheddar that the Dolomitic conglomerate formed 
two great tongues running up ravines in the older rocks, which 
had probably been due to subaérial action. Prof. Morris alluded 
to some sections which seemed to corroborate the views of 
Mr. Etheridge, and pointed out the relation of the conglomerate 
beds to the overlying strata at those points. He also mentioned 
certain peculiarities in the structure of the conglomerate itself. 
Mr. Etheridge stated in reply that the marls in the Bristol area 
were the exception, the greater part of the New Red beds being 
sandstone. 
2. ‘On the superficial deposits of portions of the Avon and 
Severn Valleys and adjoining districts.” By Mr. T. G. B. 
Lloyd, C.E., F.G.S. The author, after describing the general 
characters of what he termed the Drifts of the Upper and Lower 
series, and the freshwater gravels of the Lower Avon, comprised 
within the district of the Avon Valley between Tewkesbury and 
Rugby, and of the Severn Valley above and below the town of 
Worcester, endeavoured to show that there was a balance of 
evidence in favour of the existence of an upper and lower plat- 
form of drift in the main valley of the Lower Ayon, the upper 
one being of marine origin, and probably belonging to the same 
epoch as the stratified beds of gravel in the neighbourhood of 
Worcester, which contain marine shells and mammalian remains, 
whilst the lower one, of freshwater origin, had been derived from 
the former by fluviatile action, as supposed by the late Prof. 
Strickland. Further, that there was no evidence to warrant the 
supposition of the existence of high and low level river-gravels 
in those portions of the Severn and Avon Valleys under review, 
and that the apparent absence of any freshwater shells in the 
gravels of the Severn Valley between Bridgnorth and Tewkes- 
bury led to the inference that the freshwater gravels of the Avon 
were not represented in the adjoining portions of the Severn 
Valley, although remains of some of the same species of mam- 
malia occurred in both localities. After stating his opinion that 
the time had not yet arrived for indulging in theoretical specula- 
tions concerning the phenomena of the Drifts of the Upper and 
Lower series exhibited in so small an area as the one under con- 
sideration, the author concluded by expressing hopes that the 
facts which he had brought forward would contribute their share 
of help to the further elucidation of the question. 
. “On the surface-deposits in the neighbourhood of Rugby.” 
By Mr. J. M. Wilson, F.G.S. The author commenced by 
noticing the general configuration of the surface of the district 
under review, which he stated to consist of an elevated plateau, 
bounded and rendered irregular in its outlines by valleys. The 
district consists chiefly of Lower Lias, with a few patches of 
Middle Lias. The surface-deposits on the plateau and on similar 
high lands in the neighbourhood consist of—1. Flinty or 
quartzose drift ; 2. Sugary sand, with grains of chalk ; 3. Clay, 
with pebbles, principally of chalk, and distinctly striated. The 
valleys bounding the plateau were described as belonging to two 
systems, those of the Avon and Leam. The bottom of each 
valley is generally a narrow strip of alluvial soil, bordered by 
sand in some places, and by drift in others. The author has 
bored down into the surface-deposits in the valley of Low 
Morton. In one boring, which reached a depth of 53 feet, he 
stopped in a greyish clay containing chalk-particles ; in another, 
through similar clay to a depth of 57 feet, the rock was reached, 
and fragments of limestone were brought up. 
Mr. Searles V. Wood, jun., had long been aware of the exist- 
ence of the Middle Glacial Sand near Rugby. He pointed out 
the difference in the fauna of the sands of the Severn Valley 
below the glacial clay and those of similar deposits in the east of 
England, but notwithstanding thought they might be of the 
same age. Mr. Gwyn Jeffreys was doubtful as to the authen- 
ticity of some of the shells which had been brought to Mr. 
Maw. The fossil shells from the Severn Valley, Wolverhamp- 
ton, Manchester, and Moel Tryfaen were nearly identical, and 
indicated raised beaches. He thought it possible that a 
definite line of such beaches might eventually be recognised 
through that part of England. Mr. W. Boyd Dawkins 
did not consider that there was any marked difference in the 
mammalian fauna of the Avon and Severn Valleys. He had 
failed to discover any traces of Llefhas antiguus in either. 
Mr. Prestwich thought that the author had probably divided 
