DYNAMICAL GEOLOGY. IQI 



geological question, sometimes for the sake of physical and 

 mental relaxation. The Principles of Geology was published 

 originally in four volumes. The first volume deals largely with 

 the climatic variations in the history of the earth, and the 

 influence of these upon local physical conditions and the 

 nature of geological deposits. The second volume treats 

 chiefly of the agencies of denudation and erosion, and com- 

 prises special chapters on volcanism. The third volume 

 contains a description of coral reefs, and discusses the various 

 means by which organic remains may be preserved. The 

 fourth volume is devoted to historical geology, and as Lyell in 

 writing it adopted the results obtained in the previous volumes, 

 he produced a geological text-book upon a basis which was at 

 the time quite new. This volume was afterwards published 

 independently under the title of Elements of Geology, and 

 passed through six editions before the year 1871. 



The author's aim in the Principles is described in the 

 alternative title of the work as " an inquiry how far the former 

 changes of the earth's surface are referable to causes now in 

 operation." After an elucidation of some leading conceptions, 

 and a short but excellently written history of geology as far as 

 Cuvier and Brongniart, Lyell discusses the causes of the slow 

 development of his science, and the many false directions into 

 which it had so often been misled. 



He shows how theological prejudices and the stubborn 

 adherence to the Mosaic reckoning of time had stood in the 

 way of a right appreciation of the earth's history. The 'defec- 

 tive knowledge of physical phenomena now in operation on 

 the floor of the ocean and in the interior of the earth had also 

 served to retard the progress of knowledge respecting the 

 formation of the primitive earth-crust. But in LyelPs opinion 

 the greatest stumbling-block had been presented by the quite 

 unphilosophical hypothesis that forces different from any 

 known in the present day had been active in earlier epochs, 

 and that the physical forces still existing had in the past been 

 stronger in their action, and had produced effects which could 

 not now be equalled. Further, the supposition that the sedi- 

 mentary deposits had originally extended uniformly over the 

 whole earth, as well as the catastrophal theory of sudden 

 changes in the distribution of land and sea, in the climatic 

 relations, and in the organic creation, had, according to Lyell, 

 been hurtful to a healthy development of geology. 



