Ixxiv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



ing a younger portion of the molasse and nagelflue, with an inverted 

 dip, against the lower cretaceous rocks, and its range is indicated. 

 Sir Roderick refers to the labours of M. Studer, which will show all 

 the modifications arising from the folding of the various contorted 

 beds round the ellipsoids of crystalline rocks, modifications which re- 

 quire to be understood when the general strike of the mass is under 

 consideration. He gives a detailed account of the great inversion of 

 the masses in the Canton Glarus, by which beds of supracretaceous 

 age are brought beneath a covering of limestone containing Ammo- 

 nites, in its turn surmounted by talc slate. 



Our colleague calls attention to the necessity of most careful exa- 

 mination of the contortions and fractures (many of which he mentions) 

 before we proceed to account for the forces and the direction to which 

 such contortions and fractures may be due. A most needful caution, 

 and one which cannot be too much borne in mind in such regions as 

 the Alps. He adverts to the effects produced by the partial disloca- 

 tions and overlapping of deposits, so that the sequence is disturbed 

 in one minor region and not in another, whence the independence of 

 certain accumulations may be too hastily inferred, remarking that the 

 molasse and nagelflue present the finest example of true indepen- 

 dence of deposits in Switzerland, both lithologically and zoologically. 

 Finally Sir Roderick observes that he does not doubt " that great 

 mutations of outline have taken place at diiferent periods, not only 

 in and along the same chain of mountains in lines parallel to each 

 other, but even at different periods upon the very same line." 



Changes and Modifications which Mineral Masses may have suffered 

 since i?i the Accumulation, either before or after any Movements 

 which they may have sustained. 



Mr. Sharpe, in a second communication on the subject of slaty 

 cleavage, infers that the facts observed in connexion with this structure 

 in the mountain district of Westmoreland and Cumberland show it 

 to be due to causes solely mechanical, thus confirming his views 

 founded on the examination of slaty cleavage in North Wales, Devon- 

 shire and Cornwall, and previously brought before this Society*. 



Our colleague passes in review various facts, under the heads of 

 (1) compression of slate rocks in a direction perpendicular to the 

 planes of cleavage ; (2) two planes of cleavage in slate ; (3) slate-pencil 

 rock ; (4) cleavage not connected with crystallization ; (5) irregu- 

 larities in the direction of cleavage planes ; (6) arrangement of the 

 cleavage planes in the Cumbrian mountains, and their relation to the 

 position of the beds ; (7) northern area of elevation ; (8) southern 

 area of elevation ; and (9) conclusions, which are as follows : — 



*' The direction of the cleavage planes is in direct relation to the 

 movements of elevation of the strata, being everywhere at right 

 angles to the direction of the elevating force ; and when the beds 

 have been raised with regularity over a single axis, the cleavage 

 planes appear to be portions of curves of which the width of the area 

 of elevation is the diameter. In slaty rocks there has been a con- 

 * Quarterly Geological Journal, vol. iii, p. 74. 



