572 Proceedings of the British Association. 



the distribution and character of contorted strata all over the globe, 

 we should not be able to account very rationally for the figures they 

 assumed. — Mr. Sedgwick pointed out those circumstances in the struc- 

 ture of the Appalachian chain which accorded with previous observa- 

 tions in Europe; the persistency of the strike of the strata, the parallel- 

 ism of the anticlinal and synclinal lines, and the diminution in the 

 amount of disturbance as the strata recede from the district where the 

 greatest force was applied. He did not allow that the circumstance of 

 curvilinear elevations was opposed to the theory of M, Beaumont, 

 who had himself described curved elevations quite as striking. Most 

 of the instances adduced by Prof. Rogers, in illustration of his view of 

 the average inclination of the strata being greater on the side of each 

 flexure farthest from the centre of the disturbing forces, did not, in his 

 opinion, confirm the view the authors had taken of the origin of 

 those contortions. Again, Mr. Sedgwick stated, the position of the 

 successive strata in the British chains, was not generally such as 

 that which characterized 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 cool- 

 ing, 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 moun- 

 tains. The authors had, he thought, rather undervalued the power 

 of tangential forces. These were well illustrated in the effects produc- 

 ed 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 



