692 



J. W. JTTDD ON THE SECONDARY ROCKS OP SCOTLAND. 



lowest spring-tides. So far as I have been able to determine, after 

 several investigations of this locality, the downward succession of 

 beds below the Infralias seems to be as follows : — 



(1) Thin band of sandy clay containing irregular calcareous concretions. 



(2) Variegated marls and clays (red, greenish, and mottled). 



These strata are very thin; and it is probable that they are under- 

 lain by some conglomerate beds, which, however, are wholly con- 

 cealed in the coast- section, 



Fig. 7. — Section of PoiJcilitic Beds at Mu Geur, near the Southern 

 extremity of Sleat, Shje. 



! ! i 



LLUXUXU 



a. Torridon Sandstones. 



c. Phonolitic rock (columnar). 



b. Poikilitic strata. 



In the singularly preserved patch of Ru Geur, in Sleat, pre- 

 viously referred to, a very remarkable relic of the Poikilitic series 

 is found interposed between a foundation of Torridon Sandstone 

 and a capping of finely columnar Tertiary phonolite (see fig. 7). 

 Not more than 15 or 20 feet of the beds in question are here 

 exposed ; but so similar is the rudely stratified mass, consisting of* 

 alternating lenticular beds of fine and coarse conglomerates, com- 

 posed mainly of Torridon Sandstone, but with a fair percentage of 

 quartzite and limestone pebbles and a tolerable quantity of calca- 

 reous matter in its matrix, that there is little room for doubting that 

 these strata should be referred by us to the Poikilitic period. 



In going still farther southwards it is in Ardnamurchan that we 

 find the next exposures of the Poikilitic series ; and here they have 

 evidently reacquired some of the thickness and importance which, as 

 we have seen, they had lost in Skye. 



At Surdil, on the north coast of Ardnamurchan, we find that the 

 beds of highly contorted gneiss have their eroded hollows filled by 

 masses of angular fragments of the same rock ; and these are covered 

 by conglomerates and sandstones, above which appear the Infralias 

 limestones with well-marked fossils. Although it is certain that at 

 Surdil the Poikilitic beds are present and of considerable thickness, 

 yet so broken up are the strata by faults, so traversed and inter- 

 rupted are they by igneous dykes and sheets, and so masked are 

 their characters by metamorphic action, that it is impossible to make 



