214 RONA. GEOLOGY. 



and vice versa ; or they undergo changes still more 

 intricate, displaying those wavings and contortions of 

 which so many examples have already been recorded. 

 These rocks are as usual traversed by granite veins, 

 which, as in Coll and elsewhere, frequently present 

 the graphic character; and they alternate with simple 

 hornblende schist, or with that variety in which felspar 

 forms an ingredient. The granite veins appear so much 

 blended with the rock that it is often difficult to trace 

 the line of separation. In one o? two instances the 

 graphic granite presents a peculiarity of structure already 

 noticed in North Rona, consisting of alternate laminae 

 of quartz and felspar ; the former being occasionally 

 diminished after a certain space, so as to disappear in 

 a thin edge. 



The varieties of this gneiss are so numerous as not to 

 admit of description, but it may be remarked, that like 

 that of the Long Island, it generally possesses the 

 granitic character, being large grained ; differing however 

 in containing mica where that contains hornblende : the 

 quartz and felspar are nevertheless predominant, and are 

 often indeed the only substances entering into its com- 

 position. Like the gneiss of Tirey, lona, and Harris, 

 it frequently contains green compact felspar ramifying 

 in different directions with much minuteness of sub- 

 division. It is also conspicuous in many places for 

 the great proportion of quartz it contains, this mineral 

 possessing the chalcedonic aspect so common in gneiss. 

 In some instances the rocks are entirely formed of alter- 

 nating layers of this substance with felspar, with mica, 

 or with hornblende schist, exhibiting specimens of con- 

 siderable singularity. It may be further remarked 

 that the felspar is generally red, and that the predo- 

 minance of this colour gives a peculiar appearance to 

 all the rocks of the island. 



The felspar found in the veins, like that already 

 described in the Long Island, is often in large con- 



