582 



MR. G. W. LAMPLUGH ON THE 



[Nov. 1895, 



of lithological composition or from altered conditions of stress, seem 

 under the shear -pressure to have yielded equally throughout, and 

 in such instances the bands are now and again spread out and oblite- 

 rated for a short space, so tbat, as shown in fig. 6 (p. 571), the only 

 structure recognizable in the slaty mass is the shear-cleavage. In 

 this case it is not easy to distinguish between the effects of the 

 earlier and the later shear-pressures. The re-arranged rock, however, 

 so closely resembles the matrix surrounding the inclusions in the 

 •crush-conglomerates, that I think it may safely be considered a 

 local modification of the brecciation-stage of the earth-movements. 



Pig. 11. — Sketch-diagram showing passage of handed slate into 

 hreccia. Western bank of Sulby River (Glen Mooar) under 

 cottage opposite Slieaumonagh. (Length = 12 feet.) 



S.S.E 



N. N. W. 



®ui b 



'**i 



Firm blue and grey flaggy slates, with well-marked banding AAA, highly 

 contorted in the centre and left side of the crag, and broken up into more 

 or less rounded fragments (B B B) in a slaty matrix on the right and upper 

 part. The thickness of the bands is somewhat exaggerated in this figure. 

 C. Quartz-veins, 2 to 4 inches thick, disturbed and twisted, but con- 

 tinuous across the breccia, y-y. The later shear-cleavage. The direction 

 of movement was probably from S.E. to'N.W. 



Further evidence might, if necessary, be brought forward ; but I 

 think that sufficient has been given to prove that the formation 

 of these pseudo-conglomerates, both in regard to matrix and inclu- 

 sions, has been brought about by differential movements in a 

 variable rock-mass. It has also been shown that the conglomerates 

 occur chiefly along the junction of strata of different lithological 

 composition. And the evidence points to there having been, during 

 the brecciation of the rock, along with much sliding some actual 

 rolling or milling of the broken material. 



Considering that, in the probable original arrangement of the 

 Skiddaw strata as a whole, there has been an underlying platform 

 of grits with an overlying mass of argillaceous deposits, and that 



