ANNIVERSAKT ADDRESS OF THE PEESIDENT. 1x1 



necessarily take place — such that, assuming iron to be the substance, 

 200° the difference of temperature, and ^ ^^^^ ^^^ of the earth's mass 

 to be affected, the resulting change of volume would be not less 

 than five or six times the bulk of Vesuvius*. 



Again, the fusion of any part of the interior mass previously solid, 

 or the solidification of any part previously fluid, must occasion con- 

 siderable change of volume. According to Bischoff, granite, in pass- 

 ing from a fluid to a solid state, appears to undergo a contraction 

 from 1-0000 to -7481, trachyte to -8187, and basalt to •8960t. 



Nor is this all the effect which may be looked for from such 

 changes. The distribution of heat is modified, and the specific gra- 

 vities of adjacent masses are altered. Granting only partial solidifi- 

 cation from a fluid mass persistent beneath, we shall be prepared to 

 admit that the solid may have quite a different specific gravity from 

 the fluid out of which it has been separated J. 



Erom such causes as these now suggested, changes of level would 

 be inevitable; slow indeed and variable in position, but of long 

 duration, and of a magnitude enough to satisfy the reasonable de- 

 mands of all but cataclysmal hypothesis. 



Such, Gentlemen, are the thoughts which rise in my mind as I 

 foUow the Ariadnean thread of your annual labours. On some of 

 these weighty subjects we are not all entirely agreed ; on others we 

 have not even laid securely the basis of a lasting agreement. Let us 

 not regret this want of unity, nor stifle, under forms of general ac- 

 quiescence, the real differences of interpretation to which unlike 

 phsenomena and unequal opportunities of study ought to conduct us. 



The theory of geology is nothing less than the physical history of 

 the globe — and this history is to be extorted from the archives of 

 nature by question upon question after doubt upon doubt. When 

 geologists cease to inquire, when a dogma is quoted to relieve a 

 doubt, when faith in the dictum of some favourite author outweighs 

 the evidence in the book of nature, we may indeed have much of 

 form in our geology, but little of truth and energy — " Ipsique caeci, 

 aliorum oculis videmus, si quid." 



Ours is no coasting voyage by the sunny shores of some well- 

 havened bay ; we steer across the undiscovered ocean of truth, with 

 compasses in need of correction, under the canopy of cloud and 

 darkness which involves the origin of things ; one only faithful guide 

 across the world of ancient force and time — the permanence of the 

 laws of nature, the perpetual obedience of natural phaenomena to the 

 constant will of the great Maker, with whom is no variableness, 

 neither shadow of turning, the same yesterday, to-day, and for ever. 



* Keport of the British Association for 1858, p. 23. 



t Bischoff (Leonhard and Bronn, N, J. 1841), quoted by Hennessy in Phil. 

 Trans. 1851. 



J PhiUips in Encyclopaedia MetropoUtana (art. Geology, 1832) and Manual 

 of Geology, 1854, p. 585. 



VOL. XT. / 



