IN GLEN TILT. 339 



body of the sienite, which forms the lower part of the perpen.!- 

 diciilar face of rock over the river, a few yards below the fall. 

 In tracing the veins, an interruption, even of a few inches, in 

 their actual substance, was scarcely any where passed over ; and 

 where any interruption was passed over, it was owing to a fis- 

 sure, or some other circumstance in the surface of the rock, of 

 such a nature as to cause no doubt of a perfect continuity of 

 the substance of the vein in its original structure. I believe 

 that the various and complex ramifications of the veins, be- 

 tween the spot in which the blast was made, and the main bo- 

 dy of the sienite, would allow the -connexion to be ti'aced in 

 more lines than one. As the veins approach the main body 

 of the sienite, they grow larger, but contain many masses of 

 the strata imbedded in them. Some of the imbedded masses 

 are of granular limestone. One of these stands nearly vertical, 

 and has its stretch about north-east ; while the stretch of ano- 

 ther, which is within a foot of it, and also nearly vertical, is at 

 right angles to this. 



91. The main body of the sienite appears on the horizontal 

 surface of the rock lor some yards to the east of the bridge ; 

 and it has been already mentioned that, where the adjoining 

 part of the rock exhibits, on its upper surface, strata intersect- 

 ed by veins of the sienite, the main body of the sienite is to be 

 seen in the lower part of its perpendicular face over the river. 

 These strata, where thus intersected, appear therefore to rest 

 upon the main body of the sienite. 



92. The substance of the veins varies much in our speci- 

 mens. Sometimes it is a sienite consisting of felspar, horn- 

 blende, and a considerable proportion of quartz, and precisely 

 similar to some specimens of the main body of sienite, taken 

 from a rock only eight yards nearer to the bridge. This forms 

 the larger veins ; but some of the smaller contain only felspar 

 and quartz ; and felspar occurs here and there alone in the 



smallest. 



