320 ME. J. B. HILL ON THE [^^g. I9OI, 



we are dealing. My previous work in the district has demonstrated 

 that, in spite of the dip being at a high angle, the members of the 

 Loch Awe Series are lying nearly flat in a gentle trough of the 

 Ardrishaig Series, and that, notwithstanding the great plication of 

 the district, a general upward succession can be established/ When 

 the stratigraphy of the area is considered it does not seem possible 

 "shat an overfold so gigantic as to completely reverse the position of 

 a mass having a breadth of outcrop of 5 miles could escape detection. 

 Further, if such an overfold could be established, although it would 

 place the vesicular varieties at the surface, fresh evidence would be 

 encountered supporting the intrusive origin of the mass, for the 

 contact- altered rocks have only been observed at the base of the 

 mass, which by this process of reversal would be brought uppermost. 



After reviewing the evidence at our disposal respecting the 

 relations and character of this interesting rock-mass, there appears 

 to be no sufficient reason for removing it from the great group of 

 epidiorites and allied rocks of Dalradian age, the intrusive origin of 

 which has been sufficiently demonstrated both in this and adjoining 

 areas. '^ Moreover, the absence among the comparatively un- 

 altered sediments of any trace of volcanic ashes or agglomerates 

 lends further support to this conclusion, especially when it is borne 

 in mind that the metamorphism in this area is never sufficiently 

 potent to mask the original rock-character. 



The smaller sills which occur among the sediments beyond the 

 boundaries of the big mass call for no special comment, consisting 

 as they do of types which find their equivalent within the mass 

 described. 



The igneous intrusions of post-Dalradian age being posterior to, 

 and having no relation with, the crush-conglomerates, require no 

 description in this paper. 



III. Description" of the Ceush- Conglomerates. 



It has been pointed out that folding of an isoclinal type is 

 prevalent over the district, and that this type of folding has in 

 some instances proceeded so far that the rock-sequence is now 

 represented by a banded zone, in which the alternations are so 

 narrow that they range from a foot to as little as an inch in thickness. 

 While in some cases the process has ended here, in others it has 

 been carried a stage farther, and the closely-packed folded bands 

 have been divided by shear-planes severing the continuity of the 

 limbs until lenticular fragments have been produced more or less 

 isolated, culminating, b}^ the rolling-out of the lenticles, in the 

 j)roduction of pseudo- or crush-conglomerates. 



These structures have been observed in the limestones, the 

 quartzites, and the epidiorites, but they are most conspicuously 

 developed where the limestone and the epidiorite are in juxta- 

 position. Sections are but rarely seen in which the various processes 



^ See my former paper, Q.uart. Journ. Geol. Soc. vol. Iv (1899) pp. 475-76. 

 =^ Ihid. pp. 476-78. 



