BRITISH 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 Volcanic Eruptions. By Mr. 

 J. A. Davies. — The theory of the author was that these phenomena, gene- 

 rally preceded by atmospheric alterations unusual in degree, were also 

 connected with them, and, indeed, caused by them. He imagined that 

 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 

 pressed against its solid parts by the repulsion of deeper-seated central 

 heat, 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 Harkness, remarked that the writer did not appear to be 

 aware of the most recent observations of the highest authorities on the subject, and 

 before a definite conclusion could he arrived at concerning the influences of atmo- 

 spheric pressure, it was necessary that a greater number of observations should be made 

 than had been made by Mr. Davies. 



The Early Conditions oe the Earth, by the Rev. Mr. Brodie, who 

 maintained the following propositions : — 1. The greater heat of the tempe- v 

 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 

 which now exists. 2. The change which seems to have been produced on 

 the metam orphic 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 temperature 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 time 

 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 be 

 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 oe 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 de- 

 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 



