324 GEOLOGICAL APPEARANCES 



about 40". These strata rest on the main rock of sienlte ; and 

 from it small veins of the sienite proceed upwards into the 

 strata, and intersect them, running sometimes parallel, and 

 sometimes transverse, to their planes. I think that the veins 

 do not any where exceed an inch in breadth, and that they 

 cannot be traced for more than a foot, owing to a covering of 

 soil ; but, though the fact is exhibited on so small a scale, it is 

 very distinct. 



53. The other instance is in a mass of gneiss and mica-slate, 

 which stands detached, at a little distance from the bank, and 

 close to the water, at 7 in the plan. Its form is somewhat py- 

 ramidal, and its greatest dimensions may be about twelve or 

 fourteen feet long, six or eight broad, and between four and 

 five hiffh. The stratification is very distinct. This mass is cut 

 by veins of tlie sienite, from half an inch to fourteen inches in 

 thickness, which branch in various directions, and run in some 

 places parallel, in others transverse, to the planes of the strata. 

 The veins may be traced all round the mass, and, on the south- 

 east side, to their connexion with the main body of sienite be- 

 low. Figure II, in Plate XIX, is a sketch of this rock taken 

 from the south-east, on the opposite bank of the river. There 

 is no attempt at perspective in it, and it must be understood 

 to represent an orthographic projection of the surface of the 

 rock upon an inclined plane, dipping towards the spectator ; 

 but care has been taken to convey a faithful idea of the rela- 

 tive position of the strata and the sienite, as actually exhibited 

 upon the surface. The strata on the west side, which rise to 

 the top of the rock, have their stretch N. 168'^ E., and their 

 dip westerly 51°. At the foot of the rock on the east side, the 

 strata dip nearly at right angles to those on the western. The 

 lines of junction between the strata and the sienite are marked 

 with great precision. Near the top of the rock, the strata that 

 dip to the west, where in contact with the sienite, are a gneiss 



containing 

 o 



