OF CENTRAL CANADA PART III. 157 



shores. Professor H. D. Rogers, in his Report on the Geology of 

 Pennsylvania, contests to some extent this usually-received view, and 

 maintains that certain inclined strata of mechanical formation were 

 originally of inclined deposition. This may be true under local or 

 exceptional, but certainly not under general, conditions. (See proofs* 

 further on.) Where, however, sands and gravels are thrown down by 

 currents and running streams, an oblique arrangement commonly takes 

 place ; but this is more or less confined to the subordinate layers of 

 which the larger beds consist, as shewn in the annexed figure. The 

 inclined layers have sometimes different 

 degrees of inclination, and even dip (in dif- 

 ferent beds of the same strata) in opposite 

 directions, indicating changes in the tidal 

 or other currents by which they were 

 thrown down. This inclined arrangement 

 is termed " false bedding," or "oblique FIG. 84. 



stratification." It may be seen in some of the ancient, and also in 

 some of the more modern deposits of this continent, as in the Chazy 

 Sandstone of the south shore of Lake Superior, and in the Post-glacial 

 sands and gravels of many parts of Canada. 



Consolidation of Sediments. Having thus rapidly traced out the 

 formation of the mechanically-formed sedimentary rocks up to their 

 deposition in the state of detrital matter on the beds of seas, lakes, or 

 estuaries, we have now to inquire how these accumulations of mud, 

 sand, &c., become hardened into rock, properly so-called. 



Most sediments hold within themselves the elements of their own 

 consolidation, in the form of particles of calcareous or ferruginous 

 matter, which act upon the other substances in the manner of a cement, 

 causing the whole to " set " or harden under water. Frequently, also, 

 a large amount of calcareous matter is derived from the decomposi- 

 tion or solution of imbedded shells and other organic remains made 

 up of carbonate of lime. In the majority of strata, and in sandstones 

 more especially, merely casts or impressions are thus left, in place of 

 the originally imbedded shells. Masses of solid conglomerate are daily 

 under process of formation in places where springs containing calca- 

 reous or ferruginous matters infiltrate through the gravels and pebble- 

 beds of our Drift deposits. Many thermal springs (as well as many 



