FOSSILIFEBOUS AND UNFOSSILIFEROUS. 



19 



by hot water. The stratified rocks are believed to have been deposited in and by water, as 

 strata and laminae of sand, gravel and clay, are now forming in rivers, ponds, lakes, and 

 the ocean. But they have subsequently been subject to cleavage and foliation ; and only a 

 small part of the stratified rocks lie in a horizontal position. The lowest, that is the 

 oldest, as a general fact, are most raised or tilted up; some indeed stand perpendicular. 

 Some of the newer or uppermost strata are horizontal. This shows that the tilting process 

 was subsequent to the deposition, and in most cases to the consolidation of the formations, 

 and that it took place at different times, so as to give the lowest the largest dip. 



A difference as great exists in the consolidation and structure of rocks. The very 

 newest consist of unconsolidated gravel, sand, and clay, forming alluvium. A little 

 farther down we come to the tertiary strata, some of which are hardened into rock, and 

 others are more or less loose and soft. Next below the tertiary we find thick deposits, 

 mostly consolidated, but showing a mechanical structure along with a crystalline arrange- 

 ment of the ingredients. These are called secondary, and transition ; though these terms, 

 especially the last, are getting out of use. Lowest of all we find rocks having a decidedly 

 crystalline structure, looking as if the different minerals of which they are composed 

 crowded hard upon one another. These rocks are called Metamorphic, Hypozoic, and 

 Azoic. 



FOSSILIFEROUS AND UNFOSSILIFEROUS ROCKS. 



The term Fossil is extremely difficult to define. Upon 'the whole we prefer that 

 definition which represents a fossil to be the body of an animal or plant, or any part 

 thereof, or even any trace of the same, such as a mould, or footmark, buried naturally in 

 the earth. Such bodies or impressions are called organic remains, and if changed to stone, 

 petrifactions. By this deposition a body may be a fossil, and possibly a petrifaction, even 

 if buried only last year or last month. 



FIG. 1. 



GRANITE 

 SYENITE 

 PROTOGINE 





Igneous. 



Ideal Section of the Earth's Crust. 



