332 GEOLOGICAL APPEARANCES 



78. Fifty yards below the bridge, measuring along the north- 

 ern bank, there is a large rock, (at 5) which projects farther 

 into the water than any in its neighbourhood. A little to the 

 west of this, is another rock, containing a mass of limestone 

 imbedded in the sienite. The junction of the two substances 

 takes place without any gradation, or, if there is any, it is a 

 very rapid one. 



79. The most prominent part of the large projecting rock has 

 its base formed by the main body of the sienite, and its top 

 by several considerable masses of strata, consisting chiefly of 

 hornblende-slate, with some interstratified felspar. These 

 masses appear to rest entirely on the sienite, as the sienite 

 can be traced below all round them. Some of them dip to 

 the north-east, and others at large angles to the south-west. 

 They are intersected by veins of the sienite, several of which 

 were observed to be continuous with the main body of sienite 

 below. One of these, which, though small, was very dis- 

 tinctly traced, is near the top of the rock, on the side to- 

 wards the bank. Three others may be discovered by a close 

 inspection in the steep face of the rock towards the river. 

 The mass of strata intersected by them consists of hornblende, 

 felspar, and quartz, and may perhaps with propriety be called 

 Sienitic Gneiss. One of the veins is from six to eight inches 

 broad, another about four inches, and the third about an inch 

 and a half. The substance of the two larger veins has precise- 

 ly the same characters with the sienite of the continuous main 

 rock beneath them. Wliere the small vein joins the main bo- 

 dy of the sienite, the substance of the main body, along the 

 edt^e of the stratified mass, is chiefly felspar, and so is that of 

 the vein for three or four inches ; but above this, the vein is of 

 a sienite similar to the common sienite of the rock below. 

 The stratified masses separated by the larger veins exhibit no 



remarkable 



