420 ME. J. DURHAM ON THE VOLCANIC EOCKS 



and would seem to indicate extensive eruptions : but the lavas of 

 that period being superimposed upon the andesite have for the most 

 part been removed by denudation, leaving only the channels through 

 which they flowed to the surface as monuments of their activity, 

 though some of the tuffs seem to belong to the melaphyre eruptions. 

 The highly altered basalt dykes do not, as a rule, resist denudation 

 so well as the andesites, and are consequently often represented by 

 trenches in these rocks, the instances in which they form walls 

 being generally the denuded remains of very broad dykes, of which 

 only portions remain, projecting from the hollows. An interesting 

 example of this is to be seen in the picturesque Grhoul's Den, 

 situated about five miles south-west of Newport, which, seen from 

 below, consists of a high mass of rock, on one side of which a burn 

 has cut its way to a great depth, and leaps down the chasm in little 

 •cascades ; on the other side of the ridge of rock the ground slopes 

 more gently. The central mass of rock is the remains of a broad 

 dyke of altered basalt, the denudation of which has formed on the 

 one side the rugged miniature glen of the stream, and on the other 

 a more gentle hollow, while the whole is surrounded by the pre- 

 vailing andesite. 



Much less frequently met with than the andesites and basalts, 

 though, when present, very conspicuous on account of its light yellow 

 or red colour, is felstone ; it also is found only in dykes and bosses, 

 and although — as it contrasts very strikingly with the black and 

 dark brown of the andesite and basalt — it is readily recognized when 

 present, I have never found any trace of it among the breccias 

 &c. associated with these rocks. 



It is quite clear that the basalt (melaphyre) and the felstone are 

 more recent than the andesite (porphyrite), as these rocks can be 

 seen cutting through the last ; but I have been unable to find any 

 direct evidence as to whether the basalt or the felstone came first. 

 So far as I can find or learn, there is no instance in this part of 

 the country of felstone cutting through basalt, or basalt through 

 felstone ; but as the succession of the volcanic eruptions among the 

 Palceozoic rocks of other parts of the country shows that the acid 

 rocks succeeded the andesite, and were followed by the basalts, it is 

 perhaps safe, in the absence of evideoce to the contrary, to assume 

 a similar succession in this district. 



As may be supposed, the aspect of miles of rock exposed in the 

 clifi's of the shore, of dark basalt cutting through darker andesite, 

 with occasional patches of associated tuffs or breccias, is a very 

 monotonous one ; this monotony is, however, agreeably relieved by 

 a somewhat interesting section, which extends from below the farm- 

 house of Scroggieside, about two miles west of Newport, Pife, to the 

 fishing- station of Jock's Hole, about two miles further to the west- 

 ward. 



At the extreme west end of the section is a great mass of felstone 

 extending some two hundred yards along the beach. 



To the eastward of the felstone, beds of sandstone, composed of 

 quartz-grains mingled with volcanic ashy material, and in some parts 



