290 mr. e. b. bailey on the [June 19 13,. 



and it appears probable that it may sometimes occur within the Ardrishaig 

 slates. Further, the black slates associated with the limestone are often feebly 

 developed and may die out altogether, so that we get the limestone and grits in 

 juxtaposition. Speaking generally, it may be stated that when the limestone 

 departs from the normal type it partakes of the character of the sediment with 

 which it is immediately associated ' [14, p. 41]. 



Again, the black slates 



' may occur above, or below, or in the limestone, and sometimes, by gradually 

 becoming more calcareous, pass into the limestone, so that no line can b& 

 drawn where the limestone ends and the slates begin ' [7, p. 474]. 



And, lastly, 



' the green slates occur on the same stratigraphical horizon as the darker beds 

 with which they are often associated, but their distribution is more local' 

 [14, p. 43]. 



From the foregoing quotations it is clear that Mr. Hill's 

 classification is somewhat vague. One circumstance which he- 

 emphasizes in all his descriptions is the essential unity of the Loch 

 Awe Group. At the same time, he recognized that the deposition 

 of the group was interrupted to some extent by contemporaneous 

 erosion, resulting in the local production of a 



' boulder-bed that occurs promiscuously throughout the series, and includes 

 fragments of each lithological type ' [14, p. 45]. 



He regarded it as likely that the ' boulder-bed ' belonged to the 

 same general phase of deposition as the coarse grits. 



Dr. Peach for several years accepted Mr. Hill's main conclusions,, 

 save that he laid considerably more stress on the evidences of local 

 erosion, and referred them all to the period during which the 

 quartzite accumulated [14, p. 56 ; 17, p. 23]. In applying this 

 view consistently, he was forced to assign many more outcrops of 

 limestone to the quartzite division than had previously been done : 

 for quite commonly the limestones of the Loch-Awe region carry 

 large quartz and felspar-pebbles, exactly like those characteristic 

 of the quartzite, and in many cases rock-fragments too. Here- 

 he came into conflict with Mr. Hill's observations : for the latter,. 

 in writing of the limestone, steadily maintained that the 



' extreme divergences in type may all be met with in the same seam ' 



[14, p. 41]. 



Another, though minor, point of difference may also be noted : 

 Dr. Peach thought that the grey and green slates and phyllites of 

 the Loch Avich district represented a reappearance of the Ardri- 

 shaig Group, whereas Mr. Hill placed them in his Loch Awe Group, 

 regarding them as a local facies of the black slates. 



Dr. Peach's position in regard to the relation of the quartzite to 

 the other sedimentary schists was based to a considerable extent 

 upon analogies drawn from other parts of the Highlands, and,, 

 although never accepted by Mr. Hill, was adopted by the rest of us 

 who were working at the time in the district. 'We were, however, 

 not in a favourable position to form a judgment, since, although 

 much of the region had been surveyed, no adequate geological map 



