492 HUM. GEOLOOV. 



there occurs a mass of which the weathered surface dis- 

 plays distinct imbedded .fragments of the same rock, 

 afthottgh, on breaking it, this appearance is barely per- 

 ceptible. This occurrence is common in the analogous 

 rocks which form the summit of Ben Nevis. In another 

 place there is a still more remarkable mass, consisting of an 

 ordinary dark basalt with fragments of the red sandstone 

 scattered at considerable distances through it and varying 

 from an inch or two to a foot in diameter. It is by no 

 means common to find trap veins entangling fragments 

 of the rock which they traverse, and still less, fragments 

 so minute as those which are to be seen in this example. 

 It is a circumstance of material importance in the history 

 of trap, and analogous instances occur in the island of 

 Muck, as well as in Seil and Bute. In some specimens 

 of a German basalt, with the locality of which I am not 

 acquainted, I have observed a similar appearance, but 

 even more interesting ; since the imbedded bodies consist 

 of fragments of schist converted into porcelain jasper. 



Notwithstanding the difficulty of determining the exact 

 nature and connexion of these masses, it is probable they 

 are portions of large veins, \vhich the ruined and encum- 

 bered nature of the surface does not permit to be traced 

 to any great extent. The reasons for this belief are, that 

 numerous and distinct veins occur throughout the rocks 

 in question ; of a small size, consisting precisely of the 

 same varieties, weathering in the same manner, and 

 breaking into fragments of similar shape. This trap 

 therefore is posterior to the augit rock and syenite, 

 although it cannot properly be called superincumbent. 



But a great body of trap, independent of this and per- 

 fectly distinct from it, both in external character and com- 

 position, is also to be seen forming a very large portion 

 of the island. It is among the uppermost of all the rocks, 

 and many opportunities fire afforded of tracing its supe- 

 riority, if the requisite attention be not wanting. It 



