406 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [JunC 16, 



Its northern limit in the Lake of the Woods is the south side of 

 the great Promontory and its adjacent islands. 



Eastward it is met by granite and gneiss about Windy Point, and 

 is buried under rice-marshes. 



The western boundary is only to be found in the far west on the 

 east flank of the Rocky Mountains. 



Southward it probably underlies the whole course of Rainy River, 

 eighty miles in length, with the exception of a few outcropping bosses 

 of gneiss and greenstone ; it advances also three miles into Lake La 

 Pluie; making thus a total stretch, north and south, of 110 miles. 



I am led to believe that limestone underlies the greater part of 

 the Rainy River tract, from its universal prevalence in slabs and 

 shingle, from the uniform depth of the river, and the great fertility 

 of the country it traverses. 



8. On the Geology of the Southern portion o/* Me Peninsula 

 of Cantyre, Argyllshire. By James Nicol, F.R.S.E., 

 F.G.S., Professor of Mineralogy and Geology, Queen's College, 

 Cork. 



[Plate XXIII.] 



The peninsula of Cantyre forms one of the most anomalous features 

 in the physical conformation of Scotland, whether we regard its geo- 

 graphical or geological peculiarities. The mountain ridges which give 

 their character to other parts of the country have all, more or less, 

 a direction from north-east to south-west. On the other hand, this 

 peninsula runs nearly north and south from the Crinan Canal to the 

 Mull, a distance of fifty-five miles, with an average breadth of only 

 six to eight miles. It thus forms a narrow ridge of no great ele- 

 vation, separating the Firth of Clyde from the open expanse of the 

 Atlantic, whose waves during storms from the west beat with awful 

 fury on its western shores. None of its mountains rise high, and in 

 some places it is almost separated into several islands by low trans- 

 verse valleys. Thus at Loch Tarbet the isthmus is only about a mile 

 in breadth, and both there and at Campbeltown a depression of a few 

 feet would convert it into several detached islands ; which was pro- 

 bably its condition at no very remote geological date. Although 

 forming a portion of the Scottish Highlands, its termination lies 

 further south than some parts of the north of England. 



The most remarkable geological feature of this district is the sud- 

 den extension to the South of the mica-slate formation, which, after 

 running nearly in a direct W.S.W. line from the east coast at Stone- 

 haven through the whole Highlands, bends sharply round to the south, 

 and runs down to the extreme point of the peninsula. At the same 

 time, the clay-slate, which had hitherto accompanied it, also turns 

 south-east round the granite of Arran, and does not again appear in 

 connection with the mica-slate. In all geological maps also the Lias 

 formation is marked as occurring in this place, forming as it were a 



