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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Feb. 6, 



westerly dip of the slates at Sanaig Point in 

 Islay, however, we see the beginning of the 

 curve, which is doubtless continued towards 

 the north-east until it joins the line of section 

 already described at Loch Eil. 



One or two localities along the north-eastern 

 prolongation of the Islay series were examined 

 by us in detail, and present features of suffi- 

 cient importance to merit separate notice. 



Seil and Easdale. — These islands consist 

 fundamentally of clay-slate belonging to the 

 upper schistose series, and lying on the same 

 general horizon with the schists and slates 

 which range along the eastern shores of Islay 

 and Jura. The slates have a general south- 

 easterly dip, and range into Lorn, but are 

 there buried beneath a mass of later igneous 

 rocks, and partly also under a series of reddish 

 sandstones and conglomerates. 



Easdale consists entirely of slate, with the 

 exception of certain N.W. and S.E. green- 

 stone-dykes. Seil presents a greater variety : 

 its north -western half consists of an outlier of 

 the Lorn trap, resting, apparently conform- 

 ably, on some sandy conglomerates which lie 

 in complete unconformity on the slates. 

 These conglomerates form part of the same 

 series which in Lom, as around Oban and 

 along Loch Feochan, underlie the igneous 

 rocks and cover over the slates unconform- 

 ably. 



The annexed section, fig. 21, explains the 

 structure of this island. Without cumbering 

 the present memoir with details, it may be 

 enough to remark that the slates vary in dip 

 from S. 40° E. to S. 64° E., and the angle from 

 25° to 82°. In a hue passing a little north- 

 west of Kilbrandon Church, and reaching 

 the north-east shore near some old slate- 

 quarries, there appears to be a slight fold ; 

 but, with this exception, no instance was met 

 with of an inclination to north-west. The 

 south-east limb of the island has a strongly 

 marked ridge running parallel to the strike of the strata. It ex- 

 actlv resembles the ridges along the eastern flank of the Islay moun- 

 tains, and consists, like them, of a magnesian greenstone which 

 has been intruded parallel to the bedding. This rock is traversed 

 here, as in Islay and Jura, by transverse N.W. and S.E. dykes of 

 o-reenstone or basalt. These dykes also cut through the conglome- 

 rates as well as the sheet of greenstone to the north-west. They 



