GEOLOGY. 357 



there is eight inches more of water there than there was twenty-five years 

 ago. The other draws his conclusion from the depth of water upon the reef 

 of rocks in the river below New Brunswick, and the depth upon the middle 

 ground near Amboy, and from the action of the centre-board of the vessel 

 which always touches at these points, he is satisfied that the water is deeper 

 than it was thirty years since ; but he thinks not six inches deeper. The 

 opportunities for accurate observation arc much less frequent here than in 

 the southern part of New Jersy, but from the phenomena of the marshes and 

 of the submerged forests on Long Island and in nothem New Jersey, I 

 should infer that there was no material difference in the rate from that 

 already deduced. 



ON THE EXISTENCE OF FORCES CAPABLE OF CHANGING THE SEA- 

 LEVEL DURING DIFFERENT GEOLOGICAL EPOCHS. 



If, in assuming its present state from an anterior condition of entire fluid- 

 ity, the matter composing the crust of the earth underwent no change of 

 volume, the direction of gravity at the earth's surface would remain un- 

 changed, and consequently the general figure of the liquid coating of our 

 planet. If, on the contrary, as we have reason to believe, a change of vol- 

 ume should accompany the change of state of the materials of the earth 

 from fluidity to solidity, the mean depth of the ocean would undergo 

 gradual, though small changes over its entire extent at successive geolog- 

 ical epochs. This result is easily deduced from the general views contained 

 in other writings of the author, whence it appears, that if the surface stra- 

 tum of the internal fluid nucleus of the earth should contract when passing 

 to the solid state, a tendency would exist to increase the ellipticity of the 

 liquid covering of the outer surface of the crust. A very small change of 

 ellipticity would suffice to lay bare or submerge extensive tracts of the globe. 

 If, for example, the mean ellipticity of the ocean increased from one three 

 hundredth to one two hundred and ninety-ninth, the level of the sea would 

 be raised at the equator by about 228 feet, while under the parallel of fifty- 

 two degrees it would be depressed by 196 feet. Shallow seas and banks in 

 the latitudes of the British Isles, and between them and the pole, would 

 thus be converted into dry land, Avhile low-lying plains and islands near 

 the equator would be submerged. If similar phenomena occurred during 

 early periods of geological history, they would manifestly influence the 

 distribution of land and water during these periods, and with such a direc- 

 tion of the forces as that referred to, they would tend to increase the pro- 

 portion of land in the polar and temperate regions of the earth, as com- 

 pared with the equatorial regions during successive geological epochs. 

 Such maps as those published by Sir Charles Lyell on the distribution of 

 land and water in Europe during the tertiary period, and those of M. Elie 

 de Beaumont, contained in Bcudant's " Geology," would, if sufficiently ex- 

 tended, assist in verifying or disproving these views. Professor Hennessy. 

 Proc. British Association, Dublin. 



