V^ol. 57.] CRUSH-CONGLOMEKATES OF ARGYLLSHIRE. 319 



alternating repeatedly Avith strips of igneous material thickly- 

 studded with porphyritic felspars. The bands of alternation, both 

 sedimentary and igneous, range from an inch to a foot in thickness. 

 That the banding is due to repetition by folding can be readily seen 

 by the 'nosing-out' of the folds, though the section presents an 

 appearance of perfect regularity, with the dip highly inclined. This 

 composite zone of plication extends for a few yards, and there are 

 other localities where similar composite outcrops spread considerably 

 farther. In this case we are dealing with sedimentary and igneous 

 materials of so unaltered a type that no question arises as to 

 their character, and it is solely due to the fact that the banding 

 occurs in rocks so fundamentally different that the phenomenon 

 can be detected. 



With such examples therefore in the district, showing how minutely 

 the rocks may be interfolded while at the same time retaining an 

 evenly-bedded appearance, the apparent magnitude of the banded 

 igneous material must be received with caution. In describing the 

 section at Eilean Liver it was noted that thin strips of limestone 

 occurred among the banded igneous rock. The nearest limestone 

 sufficiently large to be drawn on the 6-inch map is 400 yards 

 distant, and it is probable that the strips of limestone are here 

 interfolded and derived from a former extension of the limestone- 

 outcrop, either above or below the present ground-surface. 



Besides epidote, tiny crystals of a lb it e, similar in appearance to 

 the albites occurring among the mica-schists in Cowal, have been 

 occasionally observed, both in the unaltered rock and its meta- 

 morphosed equivalent. 



The mapping shows that the epidiorite-mass reposes indiscri- 

 minately on the different members of the Loch Awe Series, but its 

 base appears to coincide in a general way with the horizon of the 

 limestone. It has produced contact-metamorphism in the limestone, 

 the black slates, and the quartzites. The fact of its resting in- 

 differently on each member of the Loch Awe Series need not 

 necessarily imply that it was not contemporaneous, as the sediments 

 may pass laterally into one another, and there is evidence indeed 

 that this is sometimes the case. Yet when the relations of the 

 igneous to the sedimentary rocks are critically examined over 

 the whole area it is impossible to resist the conclusion 

 that the rock is intrusive. 



While the occurrence of vesicles would at first sight suggest that 

 we are dealing with a contemporaneous rather than an intrusive 

 rock, yet when this evidence is carried further it tends rather to 

 support the view that the rock is intrusive. Field-evidence shows 

 that the vesicular varieties occur at the base of the mass, and although 

 in such a folded area it cannot always be demonstrated that these 

 types occupy this position, yet it can often be shown conclusively 

 that such is the case. Of course, the possibility of a complete 

 reversal of the sill by folding has to be taken into account. But 

 while this may often happen to the smaller sills, it is hardly likely 

 to do so in the case of a mass of such magnitude as this with which 



