CHAPTER III. 



UN STRATIFIED OR IGNEOUS ROCKS. 



THESE differ wholly from the stratified rocks 1. By 

 absence of true stratification, i. e., lamination by sorting 

 of material. 2. By absence of fossils. 3. By a crystal- 

 line or else a glassy texture instead of an earthy texture. 

 4. By mode of occurrence, as explained below. 



Origin. All these characteristics are the result of their 

 mode of origin. They have consolidated from a state of 

 fusion or semi-fusion, and poured out from below, instead 

 of deposited as sediments from above. Their original 

 fused condition is shown by their crystalline or glassy 

 texture, by their occurrence injected into fissures, or even 

 tortuous cracks, and by their effects on the stratified rocks 

 with which they come in contact. 



Mode of Occurrence. They occur in three main 

 positions : 1. Underlying the stratified rocks and appear- 

 ing on the surface in great masses, especially in mountain- 



Eruptives. 

 El Granitics. 

 ~^1 Metamorphic. 



Palaeozoic. 

 io Mesozoic. 



Cenozoic. 



FIG. 121. Ideal section of the earth's crust. 



