454 



THE GEOLOGIST. 



with a great approach to accuracy, and, moreover, that this chord might be 

 easily drawn on his diagram, because twenty-seven, i. <?., ten and seventeen, 

 being also equal to three times nine ; it is extremely easy to divide the circle 

 in the manner required by using its radius in the ordinary way. A diameter 

 bisecting this chord at right angles, and drawn to the supposed centre of the 

 water-hemisphere, forty-three degrees south latitude, necessarily passes both 

 through the geometrical centre of the earth, and through its centre of gravity. 

 As the basis of this construction of the diagram, it was assumed that the two 

 constituent areas of the earth's surface, consisting of land and water, are as 

 the squares of the arcs by which they are bounded. 



The author briefly controverted the statements of Peterman and Sir John 

 Herschell, who ascribe the appearance in question to " tumefaction," or the 

 " superior intensity of the causes of elevation in northern latitudes, and in 

 former geological epochs," observing that if earthquakes and volcanos are evi- 

 dences of such superior intensity, the elevated land ought to be on the oppo- 

 site side of the globe, since the volcanos are three times more numerous in the 

 water than in the land-hemispheres. He wished to ground his speculations on 

 existing facts, and regarded them as proofs that as one half of the moon is 

 probably heavier than the other half, so the earth is heavier on the water- than 

 on the land-side. He supposed the greater weight on the water-side to be 

 produced partly by an excess of mineral veins, beds of ironstones, and basaltic 

 rocks, with others of high specific gravity on that side, and partly by an excess 

 of hollows and cavities filled with water on the other side. Hence would 

 result the conclusion, admitted by Sir J. Herschell, that the earth's centre of 

 gravity is different from its centre of form, or geometrical centre. The author 

 was proceeding to show how the amount of this eccentricity might be computed 

 with some approach to accuracy, but the President expressed the opinion, in 

 which the author cheerfully concurred, that a subject, the treatment of which 

 required so much of mathematical demonstration, was better adapted to be 

 pursued in another section. 



Besides the diagram already referred to, the author showed another contain- 

 ing a list of ten of the highest mountains dispersed through the land-hemi- 

 sphere, and of ten dispersed in like manner through the water-hemisphere, for 

 the purpose of illustrating the fact that the mountains of the land-hemisphere 

 are uniformly of a much greater elevation above the sea-level than those of the 

 water-hemisphere. The heights of all these mountains were given in metres. 



The sums of the heights of the one group and of the other, by striking off 

 a cypher at the end of each, gave the average heights of the mountains in each 

 group. Regarding them as gauges for measuring the depth of the ocean, and 

 presuming that the mountains, which rise above submerged continents in the 

 water-hemisphere, and present their summits in the form of innumerable islands, 

 are, generally speaking, and relatively to the solid sphere of the earth, equal in 

 elevation to the mountains of the land-hemisphere, the author drew the con- 

 clusion that the general depth of the ocean (its central portion) may be taken 

 as approaching to two kilometres, and that the depths much exceeding this 

 must be attributed to local disturbance. 



ON ISOMETRIC LINES, AND THE RELATIVE DISTRIBUTION OF 

 THE CALCAREOUS AND SEDIMENTARY STRATA OF THE CAR- 

 BONIFEROUS ROCKS OF BRITAIN. 



By Edward Hull. 



As it is intended that this paper shall be laid before the Geological Society of 

 London, only a short abstract can be presented here. 

 The author endeavoured to show that during the Carboniferous period a barrier! 



