a is deduced, namely, certain weights of argentic chloride and magnesic pyrophosphate, are, if singly considered, new with each experiment; they depend on time, rate of heating, the state of division of the nitrate, and other conditions. But, assuming the results to have been brought about under a law of chemical action, the values of a must be independent of those circumstances, by which the primitive numerator and denominator could have been only pari passu affected; they are related only to the actual occurrence of the reaction. This property, in a chemical ratio, has not, it is believed, been previously observed.

After describing the means employed for obtaining a current of dry air, the apparatus required for the reaction, and the individual experiments which were severally made, the following Table of results

is given, Σ being the symbolic value of a nitrate, and Q=

Σ

a

The above list probably contains all the metallic nitrates that can be completely dried, excepting nitrates derived from amines and amides, which, in the present state of our knowledge of the phosphamides, it was evidently advisable to exclude.

In the silver group, the mean value of Q is 31.11; and the following equation may be accepted therefor :

Hence, within each set of nitrates, chemical activity is in direct proportion to symbolic value. It is further sufficiently apparent that (excepting rubidic nitrate) a and Σ increase and diminish in the same general order. Within the limits of error, the Q column is an incomplete arithmetical series, the most probable value of whose first term is 6.258, so that

m being integral.

Q=m 6.258,

Reasons are then adduced for identifying the number 6.25 with Dulong and Petit's constant of specific heat. Moreover, since the product of specific heat and symbolic value is,

generally, n 6.25, and m is greater than n, taking m=xn and s=the specific heat of a nitrate, we have

the expression for chemical activity in terms of specific heat. Comparing the coefficients (a, a') for any two nitrates, the following relations are obtained:

x's'

and it is shown that these formulæ agree sufficiently well with experiment. Where m=m' and x=x', we have the simple expression

a Σ s'

=

a Σ S

The values of Q are strictly equivalent to each other in point of activity. The author believes that a is commensurate with the elective function of chemical attraction, first discovered by Bergman. He terminates the memoir with a reference to some well-known instances of chemical action (such as that of argentic nitrate on a mixture of aqueous potassic chloride, bromide, and iodide) as serving to bestow a presumptive generality on his principal conclusions.

GEOLOGICAL SOCIETY.

[Continued from p. 76.]

January 12th, 1870.-Prof. Huxley, LL.D., F.R.S., President, in the Chair.

The following communications were read :

1. "On the Geological Position and Geographical Distribution of the Reptilian or Dolomitic Conglomerate of the Bristol Area." By R. Etheridge, Esq., F.G.S., Palæontologist 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 obtained, and then described their mode of occurrence and distribution 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 production of certain minerals, such as calamine and hæmatitic iron-ores, and discussed at some length the probable course of the phenomena of

Mr. J. Prestwich on the Crag of Norfolk and associated Beds. 137 denudation which furnished the materials for the formation of the conglomerate at different levels, in which he recognized two great periods of oscillation, the first witnessing a downward movement of the Paleozoic lands and lasting throughout 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.

2. "On the Superficial Deposits of portions of the Avon and Severn Valleys and adjoining Districts." By T. G. B. Lloyd, Esq., 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 platform of drift in the main valley of the Lower Avon, 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 Tewkesbury 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 Mammalia occurred in both localities. After stating his opinion that the time had not yet arrived for indulging in theoretical speculations concerning the phenomena of the Drifts of the Upper and Lower series exhibited in so small an area as the one under consideration, 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.

3. "On the Surface-deposits in the neighbourhood of Rugby." By J. M. Wilson, Esq., F.G.S.

January 26th, 1870.-Prof. T. H. Huxley, LL.D,, F.R.S.,
President, in the Chair.

The following communication was read:

"On the Crag of Norfolk and associated Beds." By Joseph Prestwich, Esq., F.R.S., F.G.S.

The author commenced by referring to his last paper, in which

he divided the Red Crag into two divisions-a lower one, of variable oblique-bedded strata, and an upper one, of sands passing up into the clay known as the Chillesford clay. In 1849 he had alluded to the possibility of this clay being synchronous with the Norwich Crag. He has since traced this upper or Chillesford division of the Red Crag northwards, with a view to determine its relation to the Norwich Crag. He has found it at various places inland; but the best exhibition of it occurs in the Easton-Bavant Cliff. He there found in it a group of shells similar to those at Chillesford, and under it the well-known bed of mammaliferous or Norwich Crag, with the usual shells. The author also showed that in this cliff and the one nearer Lowestoft traces of the Forest-bed clearly set in upon the Chillesford clay. He traced these beds at the base of Horton Cliff, and then passed on to the well-known cliffs of Happisburgh and Mundesley. He considered the Chillesford clay to pass beneath the Elephant bed, and to represent some part of the Forestbed. The same clay may be traced to near Weybourne. The Crag under these beds he referred to the Chillesford sands. Mention was then made of the sands and shingle above the Chillesford, for which the author proposed the names of "Southwold Sands and Shingle." These, usually, are very unfossiliferous; but at two or three places near Southwold the author found indications of an abundance of shells (Mytilus &c.) and Foraminifera in some ironsandstones intercalated in this series. In the Norfolk cliffs these beds contain alternating seams of marine and freshwater shells. The inland range of the beds to Aldeby, Norwich, and Coltishall was next traced, and the Chillesford clay shown to be present in each section, and the sands beneath to be referable to the Chillesford sands, as already shown by other geologists, on the evidence of the organic remains. Mr. Gwyn Jeffreys, who had carefully examined the shells of the Norwich Crag for the author, stated that a considerable number of arctic species were found in the Norfolk Crag which did not occur in Suffolk. While, therefore, the Norwich Crag seems to be synchronous with a portion of the Suffolk Crag, that portion is the upper division; and therefore the triple arrangement proposed by Mr. Charlesworth and advocated by Sir C. Lyell, together with the fact of the setting in of a gradually more severe climate, pointed out by the late Dr. Woodward and by Sir C. Lyell, are confirmed.

Mr. Prestwich then referred to the origin of the materials of the Southwold shingle, and showed that, with few exceptions, they came from the south. In it he had found a considerable number of worn fragments of chert and ragstone from the Lower Greensand of Kent. He considered this a convenient base-line for the Quaternary period, as then commenced the spread of the marine gravels over the south of England, and soon after commenced the great denudations which have given the great features to the country.

February 9th, 1870.-Prof. Huxley, LL.D., F.R.S., President, in the Chair.

The following communications were read :—

1. "On the Fossil Corals (Madreporaria) of the Australian Tertiary Deposits." By P. Martin Duncan, M.B. Lond., F.R.S., Sec. Geol. Soc., Professor of Geology in King's College, London.

The author noticed the history of our knowledge of the SouthAustralian Tertiary Deposits, and indicated the general distribution of the fossiliferous beds from which the corals forming the subject of his communication were derived. These were said to be confined to the region west of Cape Howe, prevailing especially in the province of Victoria, where they had been admirably surveyed by Mr. Selwyn and the officers under him, and to consist chiefly of limestones covered, and in some cases underlain, by great outflows of basalt. The author then gave a list and descriptions of the species (31 in number) of fossil Madreporaria obtained from these SouthAustralian Tertiary beds, followed by remarks on the characters and relations of the more remarkable forms, and on the localities where they have occurred. From his examination of these fossils, he objected to the application of the divisions adopted in European geology to the deposits in which they are found. He then compared the assemblage of corals obtained from the South-Australian Tertiaries with those found in various deposits elsewhere, or living in the existing seas. The species were stated not to belong to reef-building forms, but to such as now occupy the sea-botton from low springtide mark to the depth where Polyzoa abound.. Of these, 20 genera were said to be now represented in the Australian seas; but only three of them to have species in the Tertiaries, viz. the cosmopolite Trochocyathus, Flabellum, and Amphihelia. The fossil species of these were stated to be quite distinct from those now living in the neighbouring sea. Two species, viz. Flabellum Condeanum and F. distinctum, are living in the Chinese, Japanese, and Red Seas; the author's Plecotrochus elongatus is very nearly allied to the Chinese P. Condeanus; and a Deltocyathus is regarded by the author as only a varietal form of a living West-Indian and European Miocene species (D. italicus). Three species are common to the Australian and European cainozoic deposits. Several of the species were said to present curious anomalies of structure, such as so frequently appear in Australian forms, and those of the different beds to exhibit so close a general resemblance, that they offer no evidence of great changes having taken place during the deposition of the whole series of sediments. The evidence afforded by the fossil corals led the author to conclude that, at the time of the formation of these deposits, the central area of Australia was occupied by sea, having open water to the north with reefs in the region of Java, and with openings into the Mediterranean and Sahara to the north-west; that Continental India did not form part of a great continent; that the greater part of America was submerged, and the Caribbean sea a coral-area; that the bulk of the land was situated in the north and south; and that

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