OF CENTRAL CANADA PART V. 331 



Clinton beds, a steep escarpment of Niagara limestone runs through 

 the central part of the island, facing the north, following in its strike 

 the same east and west direction as the other formations of the district- 

 From the top of the escarpment, the limestones extend in a series 

 of steps to the south shore, where they become covered in places by- 

 patches of semi-crystalline dolomites belonging to the Guelph for- 

 mation. The southern portion of the Great Manitoulin is thus 

 occupied entirely by these Upper Silurian strata, and broad shelves 

 of bare limestone-rock form large portions of its surface. A con- 

 tinuous outcrop occurs along this south shore ; but the best exposures 

 are seen in the lower beds along the line of escarpment, more especially 

 about Lake Manitou and Lake Wolsey (and intervening country), 

 and around the south shore of Bayfield Sound. Cockburn Island? 

 immediately west of the Great Manitoulin, is also underlaid through- 

 out its whole extent by Niagara limestone. 



The other formations recognized within the district consist of 

 Drift clays and higher sand deposits the " Algoma Sand " of the 

 Geological Survey. The clays appear to belong essentially to the 

 lower or unstratified Drift. They occur in great thickness upon St. 

 Joseph's Island, and are overlaid very generally on Cockburn Island 

 by the higher Algoma sands. Both divisions are also seen on the 

 Great Manitoulin and elsewhere throughout the district. Detached 

 boulders, mostly of Huronian rock, occur likewise in many places ; 

 and glacial striae and furrows are seen on almost all the exposed rock- 

 s urfaces. The striae have a general south-westerly direction, but vary 

 from a few degrees west of south to about S. 50 W. 



Petroleum springs occur both on the Great Manitoulin and on 

 some of the other islands of the Manitoulin group. The petroleum 

 appears to come from the Utica shales ; but although the formation 

 has been penetrated and even traversed by several wells or borings, 

 no permanent supply has hitherto been obtained. 



THE NORTHERN PALAEOZOIC AREA. 



This area comprises a large extent of comparatively flat country, 

 ranging around the south shore of James' Bay to beyond the Pro- 

 vince boundary on A Ibany River, and stretching from these points in 



