364 Proceedings of the British Association. 



Again, Mr. Sedgwick stated, the position of the successive strata 

 in the British chains, was not generally such as that which char- 

 acterized the chain so carefully described by the authors of the 

 paper. The effects of disturbing forces, such as the intrusion of 

 igneous rocks, was chiefly dependent on the nature of the rocks 

 affected. In Cumberland, the porphyritic rocks, which were 

 evidently molten when introduced, had become hard by cooling, 

 and had been fractured and dislocated along with the rocks among 

 which they were intruded ; but from the very nature of those 

 rocks, they could not be thrown into many undulations. In 

 North Wales, where the conditions differed, and the igneous rocks 

 were less abundant, the alternating beds of solid porphyry and 

 softer rocks were thrown into a series of anticlinal and synclinal 

 lines ; whilst in the Liege country the beds, when in a very soft 

 and plastic state, had evidently been subjected to great lateral 

 pressure, forcing them to assume enormous contortions, but never 

 elevating them into mountains. The authors had, he thought, 

 rather undervalued the power of tangential forces. These were 

 well illustrated in the effects produced upon the soft slates of 

 North Devon, by the intrusion of masses of granite many miles 

 across, like that forming the forest of Dartmoor, between which 

 and other granite masses, the strata were crumpled and thrown 

 into innumerable undulations. He believed there was very little 

 analogy between the phenomena produced by earthquakes and 

 those attributed to continental elevation ; the oscillations of the 

 earth's surface produced by earthquakes were like those of a cord 

 struck when subjected to tension : from the very nature of these 

 vibrations, they might be propagated rapidly over a great part of 

 the globe. The impulses of elevation, as far as any thing was 

 known of them, were slow, acting over wide areas, and disrupt- 

 ing and contorting mountain masses. Nothing was more certain 

 than that continental masses had risen and were rising in our 

 time : Norway, for example, with curvations so slight as to be 

 invisible. In the Southern and Pacific Ocean, Mr. Darwin had 

 pointed out large areas rising and subsiding, some of them three 

 thousand or four thousand miles in diameter. He stated that he 

 was not prepared to grapple with a theory which was so imper- 

 fectly explained, and without diagrams ; he only wished phe- 

 nomena not to be pressed into its service, which either bore not 

 upon it at ail, or were perhaps opposed to it — namely, the phe- 



