AN OUTLINE OF THE GEOLOGY OP ONTARIO. 581 



continuous belt around the southern and western limits of the district. 

 The Calciferous strata are mostly dolomitic and arenaceous limestones, 

 and they extend over a considerable area along the inner edge of the 

 Potsdam belt. The Chazy strata (mostly limestone) form a broad zone 

 east of the calcifet-ous area; and the Trenton limestones, with succeed- 

 ing bituminous shales of the XJtica Formation, and Hudson River are- 

 naceous beds, occupy smaller areas towards the central and eastern por- 

 tions of the district. These Silurian beds are overlaid very generally 

 by clays and sands belonging to the Drift and Post-Glacial periods. 

 The fossil shells in the latter are all of existing species, and of ma- 

 rine or estuary type. The principal economic minerals of the district 

 comprise the dolomitic limestone of ISTepean (Chazy formation), from 

 which the celebrated "Hull cement" is manufactured; beds of the 

 same formation from near L'Orignal, which admit of a good polish; 

 and the great peat deposits of Cumberland, Plantagenet, Gloucester, 

 and adjacent townships. 



The Gananoque and Back Townships district, lying immediately 

 west of that just described, is of a very different character. In place 

 of undisturbed limestones and other palaeozoic strata, we have here 

 great beds of hard crystalline rock, mostly tilted at high angles, and 

 otherwise contorted and disturbed. The district forms a narrow belt 

 of rugged country lying along the St. Lawrence, between Brockville 

 and the vicinity of Kingston, but rapidly widening and covering a 

 large area in its northern and north-western extension. Its southern 

 boundaiy runs from the east of Kingston through the back town- 

 ships of Prontenac, Addington, Hastings, Peterborough, Yictoria, 

 and Simcoe, and strikes Georgian Bay near the mouth of the Severn. 

 From this point it forms the shore of the Bay to beyond French 

 River. Its north-western boundary is to some extent a conventional 

 line running from the latter spot to Lake Temiscamang. Strictly, 

 perhaps, the district should not be separated from that of the Upper 

 Lakes, but for descriptive purposes it is convenient to keep the two 

 distinct. They present, moreover, certain points of difference. Both 

 consist essentially of crystalline mineral regions; but in the lower 

 district the gnessoid rocks are interstratified with many bands of 

 crystalline limestone, containing various silicates and other minerals ; 

 whilst these Kmestone bands are apparently wanting in the more 

 western country. In both regions iron ores abound ; but those of the 

 lower district are frequently titaniferous, whilst those of the upper 



