1214 JURA* -GEOLOGY. 



thus proved that there is a body of trap in the vicinity of 

 the veins, of which a considerable portion is now appa- 

 rently concealed by the sea. The breadth of the strait 

 is here about two miles ; and although nothing like a proof 

 can be offered, it is not improbable that a large portion of 

 this space was once occupied by a rock which has in 

 later times been removed by the action of the sea, or by 

 other caused. In considering the revolutions which the 

 surface has every where undergone, and of which this 

 strait presents such palpable marks, in the correspondence 

 of the strata on the opposite shores, it is not very unrea- 

 sonable to suppose that Glas island is the last remaining 

 portion of a more extensive mass, which might once have 

 covered even the adjoining land on both sides, and have 

 been the origin of the veins in question. The analogy 

 between this spot and. the Maddies on the shore of North 

 Uist, is remarkable ; and the same circumstance of the 

 existence of corresponding veins, attends both. Thus also 

 it may probably be concluded, that the central trap of 

 Jura is the origin of the veins on the neighbouring coast of 

 Cantyre, of which a very remarkable collection occurs at 

 Killean, since no other neighbouring mass can be traced to 

 which they can be referred. Those of the Mull of Cantyre 

 may also possibly originate in the same source ; unless 

 Arran should here be supposed the central point from 

 which these diverge. In a general view this fact is im- 

 portant, as it confirms the rule already deduced from former 

 observations made in this country, respecting the con- 

 nexion of trap veins with extensive masses of a parent rock. 

 It serves still further to approximate the great trap district 

 of the Western isles to that of Ireland ; by interposing 

 another point which conduces to diminish the apparent 

 distance between two tracts of which the connexion may 

 once have been much more intimate than it is at present. 



With respect to the veins, separately considered, a 

 very few remarks will suffice, as they present scarcely 

 any appearances that have not been described on former 



