164 



MINERALS AND GEOLOGY 



many of these so-called valleys of elevation lie in the beds of rivers> 

 or occupy comparatively low ground. The River Humber near To- 

 ronto, for example, flows at the lower part of its course over a. 

 denuded anticlinal of this character.* Finally, it may be observed,. 



Fig. 89. 



that when strata lie in parallel beds (as in Figs. 85 and 89), the* 

 stratification is said to be conformable or concordant. When on the 

 other hand, the beds are not parallel, the stratification is said to be 



unconformable. The accompany- 

 ing section, in which the inclined 

 beds belong to the Laurentian r 

 and the overlying beds to the 

 Lower Silurian Series (see Part 

 V.), as shewn on Crow Lake, 

 north of Marmora village, is an 

 example of uncomformable strati- 

 fication, or of want of concor- 

 dance between these two series 

 of rocks. As explained further 



Fig. 90. 



on, a want of conformability indicates almost invariably the com- 

 mencement of a new geological period. 



Both horizontal and inclined strata frequently exhibit fractures of 

 greater or less extent. Mineral veins, it may be mentioned, consist 

 essentially of cracks or fractures formed at some more or less remote 

 period in the surrounding rocks, and filled subsequently by various* 

 agencies, with sparry, earthy, and metallic matters. The strata on 

 one side of a fracture are often displaced, being thrown up or do win 

 as it were. This peculiarity is technically termed a fault. The 



* Professor Robert Bell in his Report on the Manitoulin Islands, has pointed out the occur- 

 rence of fifteen anticlinals, crossing the Great Manitoulin in a general north and south direc- 

 tion. These anticlinals give rise on the north shore of the island to deep indentations or bays,, 

 and inland to a series of parallel lakes. 



