THE 



canadian- 

 NATURALIST AND GEOLOGIST. 



Vol, VIII. OCTOBER, 1863. No. 5. 



Art. XXIV — On the Origin of Eruptive and Primary Rochs ; 

 by Thomas Macfarlane. Part II. 



{Presented to the Natural History Society.) 

 II. The eruptive formations. 

 In referring to these formations, it will be impossible altogether 

 to avoid mentioning many matters, which are very generally 

 known regarding them. Still the connection of eruptive rocks on 

 the one hand with the constitution of the interior of the earth as 

 adverted to in the last chapter, and on the other hand with certain 

 slaty modifications of themselves, will be kept in view as much as 

 possible. The rocks of these eruptive formations possess, as is 

 well known, characters which distinguish them sharply from rocks 

 of sedimentary origin. While the latter have been made up of 

 the debris of rocks pre-existing on the earth's surface, the eruptive 

 formations have derived their material from beneath the earth's 

 crust. Hence they have been respectively termed by Humboldt 

 exogenous and endogenous rocks. The eruptive rocks are more 

 or less crystalline, generally but not always unstratified. The sedi- 

 mentary rocks possess opposite characters. Each eruptive rock 

 is in a high degree homogeneous and shows nearly the same char- 

 acters and composition throughout its whole mass. This is much 

 less the case with sedimentary rocks. The eruptive rocks occur 

 in very irregular forms, as enormous irregular masses, (typhonische 

 stocke) covers or caps (Kuppen or Decken), veins, streams and 

 Can. Nat. 22 Vol. VIII. 



