XXIT PROCEEDINGS OF THE GEOLOGIOM* §©€tETY. 



In your paper on the Transport of Erratic Blocks, also printed in 

 the Cambridge Transactions, you have estimated the force of great 

 sea-waves of translation, such as might arise from a sudden upheaval 

 of the bed of the ocean, and you have calculated the enormous rate 

 of increase in the transporting power of currents, according to their 

 increased velocity. I have elsewhere ventured to express my doubts 

 whether such waves have really been the principal instruments which 

 conveyed the huge boulders and erratics of the northern drift from 

 place to place ; but I hold that the value of such investigations as 

 yours does not depend on the acceptance or rejection of the particular 

 theories to which they may be immediately applied. They belong 

 to a class of researches which must be gone into and worked out by 

 mathematicians before we can pronounce positively on the suffi- 

 ciency or insufficiency of many of the causes assigned to account for 

 observed phaenomena. 



After you had discussed m your paper on Physical Geology the 

 principles on which a theory of elevation might be founded, you pro- 

 ceeded to examine the Wealden and the Bas Boulonnais, in order to 

 test your theoretical results by field observations. In a subsequent 

 memoir on the Lake District of Cumberland, published by this So- 

 ciety, you pointed out that the valleys in which the lakes originated 

 depend on a system of dislocations following a law in exact accord- 

 ance with your theoretical deductions. In the same paper you have 

 also given a series of diagrams, which exhibit with great clearness 

 your conception of the diiferent phases through which the geology 

 and geography of the Lake district must have passed during the suc- 

 cessive stages of its elevation and denudation. 



Time will not permit me to give an analysis of yom' memoirs 

 on the Mechanism of Glacial Motion, and on the Effects of the In- 

 ternal Pressure and Tension of Rocks, considered as illustrative of 

 cleavage. These subjects involve points of controversy on which 

 philosophers of high authority are still at variance. But I cannot 

 conclude without alluding to the most elaborate and difficidt problem 

 in which you have ever been engaged ; I mean your attempt to deri 

 termine whether the solid crust of the earth can be so thin as to 

 justify the hypothesis, that volcanos are in immediate communica- 

 tion with a central fluid nucleus. In grapphng with this abstruse 

 question, you begin by reminding us, that if the earth were per- 

 fectly spherical, the axis about which it rotates would preservey? 

 during its annual motion round the sim, a perfectly parallel position. 

 But as the earth is spheroidal and not spherical, the attraction of the 

 sun and moon on the protuberant equatorial portions destroys this 



