ANNUAL ADDRESS, MDCCCLXXHI. 49 



sedimentary strata are twofold 1st, the decomposition of 

 silicates containing these bases such as lime, feldspars, and 

 pyrox ; and 2ndly, the action of the alkaline carbonate, 

 formed by the decomposition of feldspars, upon the chlo- 

 rides of calcium and magnesium originally present in sea 

 water, which have thus in the course of ages been in 

 great part replaced by chloride of sodium. The clay or 

 aluminous silicate which has been deprived of its alkali 

 is thus a measure of the carbonic acid removed from 

 the air, of the carbonates of lime and magnesia precipi- 

 tated, and of the amount of chloride of sodium added to 

 the waters of the primeval ocean. 



I accept in its widest sense the view of Hutton and 

 Boue " that all crystalline stratified rocks have been pro- 

 duced by the alteration of mechanical and chemical 

 sediments." 



On the occurrence and probable origin of intercalated lime- 

 stone and dolomite Mr. Hunt writes at p. 464, " The mag- 

 nesian rocks among the unaltered sediments of the Hudson 

 River group afford an interesting study. The dolomites 

 of Pointe Levis, are interstratified with the pure limestones, 

 sandstones, and graptolitic shales of the Quebec division 

 of the Hudson River group. Both limestones and dolo- 

 mites are very irregular and interrupted in their distribu- 

 tion, the beds sometimes attaining a considerable volume, 

 while at other times they thin out, or appear to be 

 replaced with sandstones. The limestones frequently form 

 masses of many feet in thickness, which are without any 

 visible marks of stratification, and destitute of organic 

 remains. These masses are compact, conchoidal in fracture, 

 sub-translucent, and exhibit a banded agatized structure, 

 which leads to the conclusion they are chemical deposits 

 E 



