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THE POPULAR SCIENCE MONTHLY. 



tives of the first extruded lavas are penetrated by intrusions of gab- 

 bro, the granitic form of the later ejected lavas. From these great 

 intrusive masses of highly crystalline rocks proceed in every direc- 



Fig. 11. Plan of the Dissected Volcano of Mull, in the Inner Heekides. 



a Rock?, on b Great intrn- c Lava - cur- 



wbicta the give masses rente of ba- 



volcano of acid and salt which 



has been intermediate have flowed 



built up. rocks. from d. 



Fig. 12. Section of the Volcano along the Line A B 



d Intrusive e Lava -cur- / Volcanic 



masses of rents which tuffs and 



tiabbros have flowed agglomer- 



and doie- from b. ates. 

 rite. 



tion spurs or dikes, which are evidently (lie radiating fissures formed 

 during the outwelling of igneous materials from below, injected by 

 fluid substances. Besides the vertical or oblique dikes we also find 

 horizontal sheets, which, passing from the central masses, have pene- 



