THE ISLE OF E1UG. 1()1 



(the differences between them being almost of an acciden- 

 tal nature), the intrusive rocks of Eigg and the Hebrides 

 be considered as elaborated only under the pressure of 

 the atmosphere, and be this strictly volcanic, or whether 

 they have been poured forth under the compressing forces 

 of water or of rock and thus be Plutonic, in the original 

 and unchanged meaning of the term. That looseness in 

 describing, however, which styles every unstratified rock 

 volcanic (if this term means what Faujas St Fond and the 

 original volcanic school intended), we cannot vindicate, 

 inasmuch as we feel assured, that, although both classes 

 are ignigenous, there are distinctions between them both in 

 form and mineral character which render their separation 

 at once natural and apparent. As regards form, the chief 

 feature which distinguishes the two series is, that none 

 of the basaltic greenstone or pitchstone ranges can ever 

 be viewed as examples of consolidated mineral streams 

 which have issued from a crater. Boue, throughout his 

 interesting " Essai Geologique sur l'Ecosse," has noticed 

 the greater number of the rocks of the Hebrides, and 

 those of several other points of Scotland, as volcanic, and 

 designated the external aspect of the generality of trap- 

 masses under the term " Coulees," that is, streams which 

 have flowed from a volcano in the open air, and this opinion 

 has been restated in various works, both German, French, 

 and English ; with it, however, we can never agree, but, on 

 the contrary, must maintain that no one of the so-called 

 basaltic streams affords, in their form, any evidence which 

 can ever allow us to imagine that they had been erupted 

 under circumstances fitted for so free a motion of their in- 

 herent particles, as obtains when a rock has been pro- 

 truded solely under the pressure of the atmosphere. Be- 

 sides the absence of this feature in the trap-rocks of the 



