GEOLOGY, 



OEIGIN OF THE INTERBEDDED AND INTRUSIVE BASALTS' 



OF KINNOULL HILL. 



By Henry Coates. 



THE basalts and other igneous rocks which enter into the structure 

 of Kinnoull Hill are identical in chemical composition with the 

 lava streams which issue from the craters of Vesuvius and Etna, and, 

 not only so, but their occurrence, as rock masses, also points unmistak- 

 ably to the same conclusion. Two kinds of igneous rock occur on 

 Kinnoull Hill. 



Apart altogether from distinctions of mineralogical composition and 

 other lithological characters, all volcanic rocks, considered with re- 

 gard to their origin, fall into two great divisions First, those which 

 have come to the surface of the earth's crust in a molten state, and 

 have consolidated, either exposed to the air or under water ; and 

 second, those that have not come to the surface of the earth in a molten 

 condition, but have forced their way into fissures and other channels, 

 and there consolidated beneath the earth's surface. 



It is obvious that volcanic rocks formed in the first way will be found 

 resting on beds which were formed immediately prior to their being 

 poured out, and that, lying on the top of them, will be found beds 

 which were formed immediately after. They are, therefore, called 

 " contemporaneous," or "interbedded" volcanic rocks. With regard 

 to rocks formed in the second way, it is equally evident that the rocks 

 in which they occur must have been formed before the volcanic mass 



