44 Scientific Proceedings, Royal Dublin Society, 



were in approximately horizontal positions. The case is different 

 now, for the Silurian beds have an easterly dip, while the Cam- 

 brian sandstones are nearly always horizontal. It is clear, there- 

 fore, that the present horizontality of the latter is due to a second 

 tilting in a direction opposite to the first. In the accompanying 

 diagram (Plate X.,fig. 5) I have attempted to restore the beds of the 

 three formations to their positions at the time the Lower Silurian 

 rocks were in their original horizontal position. It will be 

 observed that then the Cambrian rocks had a dip westward, 

 while the original denuded surface of the Laurentian schists 

 sloped at a smaller angle in the same direction.* Upon this 

 horizontality of the Cambrian beds depends in a large measure 

 the peculiarities of the west Highland scenery, and it is doubtful 

 if a stranger series of events in stratigraphical geology is to be 

 found in any other part of the world.t 



Do Laurentian Rocks occur in the North orWest of Ireland? All 

 that one can say at this moment is, that the district lying north of 

 Gal way Bay in Connemara, Belmullet in Mayo, and parts of north- 

 west Donegal contain beds of gneiss similar in appearance and 

 composition to those which constitute the Laurentian beds of 

 Sutherlandshire, and that these beds stand in some sort of rela- 

 tionship to the recognized Lower Silurian metamorphic beds 

 consisting of quartzites, limestones and schists. But until the 

 Highlands of Donegal have been thoroughly explored by the 

 officers of the Geological Survey, and the relations of the beds 

 clearly established, no positive answer can be made to the 

 above question, the Cambrian beds being (as far as we know) 

 unrepresented.! 



* From this diagram, which was made at Queuaig (see Plate XL, fig 9), not being drawn 

 strictly to scale, I cannot be certain that the slope of the Laurentian floor is correct. 



j The peculiarities of this district have been described by Macculloch, Hugh Miller, 

 Murchison, Ramsay, Geikie, and others. 



J The author proposes to make a preliminary examination of the Donegal Highlands 

 during the ensuing summer with a view to determine the question here raised. 



