BETTISH ASSOCIATION MEETING AT NEWCASTLE. 375 
various levels in the same vertical section, and of certain peculiar pheno- 
mena connected with the structure known as " diagonal stratification ;" 
after which he proceeded to show that the conglomerates and sandstone, 
in every layer, afford evidence of their littoral origin, and of their having 
been deposited on a tidal strand undergoing slow subsidence ; and con- 
cluded with a description of two systems of dykes of Triassic sandstone, 
one of which, having a north and south direction, invariably intersects 
the other, which runs nearly east and west. 
On the Causes of Earthquakes and Yolcanic Eeuptions. By Mr. 
J. A. Davies. — The theory of the author was that tliese phenomena, gene- 
rally preceded by atmospheric alterations unusual in degree, were also 
j connected with them, and, indeed, caused by them. He imagined that 
I the matter of volcanic eruptions, which, or part of which, might be the in- 
terior surface of the earth's crust rendered fluid by fusion, was constantly 
ressed against its solid parts by the repulsion of deeper-seated central 
eat, and that this pressure was balanced by the weight of the external 
atmosphere, the equilibrium being destroyed by the rarefaction or greater 
density of the air, combined with variations in the internal heat, and that 
thus these phenomena are produced. 
The Chairman, Professor Harkncss, remarked that the writer diH not appear to be 
aware of the most recent observations of the highest autlioritics ou the subject, and 
before a defiaite conchision could be arrived at coiicerniiit!; the influences of atmo- 
spheric ])ressure, it was necessary that a greater number of observations should be made 
than had been made by Mr. Davies. 
The Eaely Conditions of the Earth, b}'- the Eev. Mr. Brodie, whi> 
maintained the following propositions : — 1. The greater heat of the tempe- 
rate and polar regions, in the earlier eras, cannot be accounted for on the 
supposition that the distribution of land and water was different from that 
whicli now exists. 2. The change which seems to have been produced on 
the metamorphic rocks was not caused by heat from within acting upon 
them while they were covered with a mass of superincumbent strata. 3. 
That we have no conclusive evidence that the teiuperature of the central 
part of the globe is higher than that of the surface. 4. That there is no 
evidence that the great mass of the earth has ever been in a fluid state. 
5. That all the phenomena hitherto observed may be satisfactorily ac- 
counted for, on the supposition that the earth was at some former timc^ 
exposed to great external heat. The general inference which he would 
deduce from his observations was that in all speculations in regard to 
the physical condition of the earth in former epochs, it should ever bo 
kept in mind that an increase of temperature implies an increase of atmo- 
spheric pressure, with all the effects on chemical combinations and animal 
and vegetable development which such an increase would produce. 
A Help to the Identification of Fossil Bivalve Shells. By Mr. 
Harry Seeley. — Students well knew that genera were practically realities, 
and as such the geologist and the zoologist had to do with them. Between 
many groups intermediate forms could not be found. The question then 
arose — How many genera are known ? Their distinctive characters di'- 
pended on the definition of a genus adopted. If it were merely a number 
of nearly-related species, then the descriptive characters would include 
those in all forms ; but if it existed independently of the species being 
fundamental to them, then the specific characters could not enter into the 
description of the genus. Practically, the latter view, adopted in this 
paper, reduced the description to a sixth of the shortest customary lengths, 
whilst the distinction became clearer by pruning away much that was 
