ANNIVERSARY ADDRESS OF THE PRESIDENT. IxxxHi 



details on the cleavage of the rocks of Valentia Island and the neigh- 

 bouring parts of Cork and Kerry, and show, from an analysis of 

 the slate, that the cleavage is most complete in those rocks which 

 contain the most alumina, and that the sj)ecific gravity is greatest 

 in the most slaty beds. They state that all their observations on 

 slaty rocks seem to confirm my deductions that " there has been a 

 compression of this mass in a direction everywhere perpendicular to 

 the planes of cleavage, and an expansion of this mass along the 

 planes of cleavage, in the direction of a line at right angles to the 

 line of incidence of the planes of bedding and cleavage, or in other 

 words, in the direction of the dip of the cleavage." — Edinburgh New 

 Philosophical Journal^ 1855. 



The next paper that I shall notice is that by Mr. J. C. Moore 

 on the Silurian rocks of Wigtownshire, in which he points out 

 the curious arrangement of the rocks which form the peninsula 

 between the Midi of Galloway and Corsw^all Point, and discusses 

 the question of the relative positions of the graptolitic schists 

 of Wigtownshire and the coarse conglomerate and limestones of 

 Ayrshire. The preceding paper of Professor Harkness has already 

 brought under notice the folded character of the Silurian strata 

 in Dumfriesshire and Roxburghshire, and in this paper it is still 

 more strikingly illustrated both in description and in the illustrative 

 sections, the strata having been bent into a series of anticlinal and 

 synclinal folds, the crown of the anticlinal in some cases being 

 still preserved. As this folded condition of the strata can be 

 observed for a distance of 30 miles, and as in the distance of 5 

 miles from the granite of Dunman to the Mull of Galloway fifteen 

 such folds occur, it may be considered a very striking and mag- 

 nificent example of this description of phsenomena. In most cases 

 the folds are thrown over to the north, so as to produce a short and 

 a long leg to the curve, the strata of the short leg, to the north of 

 the axis, being nearly vertical, whilst the strata to the south of the 

 axis slope comparatively gently to the south. This arrangement is 

 however sometimes reversed, as indeed it might have been expected 

 would be the case, unless the direction of pressure had remained in- 

 variable. In the sections two masses of granite and syenite are re- 

 presented as intruded amongst the sedimentary rocks, and the folds 

 of the strata north of the granite are represented as thrown over 

 to the north, whilst those south of the syenite are thrown over to 

 the south, the strata between the two appearing rather ambiguous 

 in their indications. The explanation of the folding of strata must 

 still be classed amongst the only partially solved problems of geology. 

 In the present example, as in the first of Mr. Moore's sections, we 

 have two masses of intruded rock occupying a space of less than 4 

 miles, and a section of 26 miles of contorted strata in relation to 

 them ; and it scarcely seems possible, as observed by Mr. Moore, to 

 consider the intruded masses as a sufficient proximate cause for the 

 effect produced, though they may be reasonably considered indica- 

 tions of a powerful internal force, which, after producing a modified 



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