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XLV. An Examination of those Phenomena of Geology, 

 which seem to bear most directly on theoretical Speculations. 

 By the Rev. W. D. CONYBEARE, M.A. F.R.S. F.G.S. fyc. 

 (Part II.) 



[Concluded from page 197.] 



Art. II. nPHE configuration of the valleys which appear to 

 * have resulted from excavation, especially the 

 intersection by transverse valleys of continuous longitudinal 

 valleys, themselves opening possible outlets to the drainage, 

 is inconsistent with the theory which assigns the drainage of 

 the atmospherical waters as the excavating agent. 



Observations. If any difficulty should be felt at first sight 

 in exactly appreciating any of the terms employed in the above 

 short general enunciation of the principle here maintained, 

 I shall trust fully to explain them in proceeding with the de- 

 tail. In the first place, I would propose to class our valleys 

 according to the apparent difference of their probable origin ; 

 although the excavating action of water may very probably 

 have materially modified them generally, yet it would be 

 clearly inconsistent with the phenomena to refer their origin 

 exclusively to this cause; the convulsive forces which have 

 acted on the surface of our planet have often dislocated its 

 strata, elevating one portion and depressing another from the 

 level of their planes of deposition, and again contorting and 

 bending them into the zigzag form of the letter (W). Now 

 in the first case the lines of subsidence, and in the second the 

 concave reentering angles, would naturally form valleys ; these 

 I would term generally valleys of dislocation : or if it should 

 be expedient to distinguish those referable to the one or the 

 other of the above cases, they may be characterized as valleys 

 of subsidence or of contortion*. On the other hand, the valleys 

 traversing the districts of which the nearly horizontal strata 

 are scarcely at all affected by dislocation f, cannot have origi- 

 nated in such causes; and if there be sufficient grounds for be- 

 lieving the strata to have been originally continuous, we must 

 of course suppose the valleys actually intersecting them, to 



have 



* While I am sending these lines to the press, an interesting analysis of 

 Professor Sedgwick's paper read at the Geological Society, On the Cum- 

 berland district, has appeared in your last Number. He describes the valleys 

 in that district as valleys of dislocation. 



f These nearly horizontal strata having been deposited at the bottom 

 of the sea, appear indeed to have been subsequently raised by some ele- 

 vating force : but in this case, such a force must have acted gradually and 

 uniformly, so as not to dislocate their planes (which remain perfectly con- 

 formable), or disturb their relative levels. Now in the objections which 



Mr. 



