Vol. Sg.'] LOCH AWE SINCLISTE (ARGYLLSHIRE). 293 



in the Tayvallich Division, together with the frequent occurrence of 

 pebbly and conglomeratic beds, may be noticed at once. Although 

 Mr. Hill did not attach stratigraphical importance to these differences, 

 he did not fail to record them [14, pp. 50-51]. Thus, in describing 

 the district lying between Loch Fyne and Loch Awe, he says that 

 the limestone, where it crops out at the margin of the Loch Awe 

 Group — that is, according to the new interpretation, in the Shira 

 position, — 



' although usually sandy, rarely exhibits the coarse gritty character seen 

 further to tbe north-west. There is either an entire absence of black slate, or 

 it occurs in very limited amount. Further, the boulder-bed has not been 

 observed at that margin, so that, speaking broadly, the occurrence of the 

 boulder-bed, the gritty limestone, and black slate in appreciable quantity 

 appear to hang together. Moreover, the marginal limestone, where not 

 associated with black slate, is seldom of the dark graphitic hue which it 

 assumes when in association with well-developed black slate.' 



To these differences it may be added that the Tayvallich Volcanic 

 Zone, with its accompaniment of breccias containing epidiorite- 

 fragments, is very strongly developed in the Tayvallich Slates and 

 Limestones, and in the adjacent portion of the Loch Avich Division, 

 but is completely unrepresented in connexion with the Shira 

 Limestone. 



(5) The associations of the Tayvallich Slates and Limestones 

 distinguish this division from the Shira Limestone. The Tayvallich 

 Division in the neighbourhood of Loch Awe is interposed between 

 the Loch Avich Slates and Grits, in the centre of the syncline, and 

 the surrounding Crinan Quartzite. The Shira Limestone, on the 

 other hand, is admittedly interbedded between the Crinan Quartzite 

 and the Ardrishaig Phyllites beyond. It is claimed that the 

 differences, cited in this and the preceding section, are a proof of 

 the stratigraphical distinctness of the two divisions. 



(6) Structurally, the Tayvallich Slates and Limestones lie above 

 the Crinan Quartzite, while the Shira Limestone lies below it. 

 This structural proposition is, of course, quite distinct from the 

 stratigraphical proposition argued above. It is based upon three 

 main sections : — 



(6 a) The relation of the Tayvallich Slates and Limestones to the 

 Crinan Quartzite is exposed to perfection in the Tayvallich penin- 

 sula, and has been described by Dr. Peach and myself in the 

 Survey Memoir [18, pp. 65-68]. The reader is referred to this 

 description for details, which are illustrated by a text-map on the 

 scale of 3 inches to the mile. The following are the main con- 

 clusions : — There is no sharp line of separation between the Tay- 

 vallich Division and the Crinan Division of the Loch Awe Group : 

 the two are united by an intermediate zone in which there is con- 

 spicuous interbedding of the various rock-types — slate, limestone, 

 and quartzite, any of which may assume a conglomeratic facies. 

 But, despite the transition-zone, the two divisions have a well- 

 marked individuality, and the Limestone-Slate Division, with its 



