276 A. GEIKIE Otf THE SUPPOSED 



obliterated, though lines of pebbles can be traced which appear to 

 indicate that the strata are nearly vertical. 



On the opposite side of the river another junction of the granite 

 -with the Cambrian beds can be seen. The latter consist of greenish 

 shales and sandstones dipping IN". 20 W. at 55°., and are here again 

 distinctly overlain by the granite, which cuts across the edges of 

 the strata that dip beneath it. At this point the line of junction 

 has served as a channel for percolating water ; and the rocks on 

 either side are so decomposed that no satisfactory observations of 

 their internal characters can be made. 



It is deserving of remark that, in its course across the valley, the 

 projecting tongue of granite now described traverses obliquely a 

 considerable thickness of strata. In particular, it can be seen to 

 have cut out nearly the whole of the thick bed of grit above 

 referred to, no portion of which • appears on the opposite side 

 (figs. 4 and 5). 



Fig. 4. — Plan of Junction of Granite with Cambrian Strata, 

 Porth-clais. 



The eastward prolongation of the Porth-lisky granite mass 

 likewise protrudes as a tongue into the Allan valley. This tongue 

 has a breadth of about eighty yards ; but it seems to be narrowing 

 eastwards, so that, as already stated, it probably does not cross the 

 valley. On both its northern and southern borders its junction 

 with the Cambrian rocks can be seen. On the south side greenish 

 sandstones, shales, and silky hydro-mica schists, like some of those 

 to be afterwards referred to as occurring at Porth-lisky, abut 

 against the granite ; but the rocks along the line of contact have 

 been decomposed into clay by the rise of water. On the north side 

 the junction is more satisfactorily shown in a quarry on the left side 

 of the road from Porth-clais to Rhoscribed. Here the conglomerate, 

 in highly inclined beds, is overlain by the granite, which leans 

 against it. The conglomerate is indurated; but at the actual 

 contact both rocks have been much decomposed by percolating water. 

 Some of the details of these junctions of the granite with the 

 stratified rocks are reserved for the second part of this paper (p. 317). 



Before leaving the relations of the granite to the Cambrian strata 

 in the Allan valley, I must allude to the fact that this is the locality 

 cited by Dr. Hicks as showing the Cambrian conglomerates and 



