128 KEV. E. HILL AND PEOF. T. G. BONNET ON THE 



to which, as they appeared to be the most suggestive, we gave 

 much attention. 



This horublendic rock occurs in masses varying in volume from 

 several cubic yards downwards. In form these exhibit every 

 gradation from lenticular lumps and angular irregularly- shaped 

 blocks on the one hand to shreds and streaks on the other. That in 

 certain cases the rock has been shattered and pierced by an intrusive 

 rock of a very different mineral character seems beyond question. 

 The most conclusive evidence is afforded by the cliffs south of 

 Dixcart Bay, when they are examined from a boat. One crag (? JS'oir 

 Eec), about 80 feet high, is a gigantic breccia from crest to foot. 

 When the hornblende-rock occurs in angular masses the intruder is 

 a pale flesh-red granite, poor in mica, but as the former rock becomes 

 more lenticular in outline, the latter becomes greyer, more mica- 

 ceous, and rather darker in colour, until at iast the two are 

 associated in a manner curiously resembling a kind of current- 

 bedding,^ and suggestive of stratifi.cation rather than of intrusion. 

 Masses of this coarse hornblendic rock also occur (though less 

 frequently and, as we think, usually of a lenticular form) among 

 the normal hornblende-schist. 



(a) Section at the eastern corner of Point Derrihle. — This section, 

 unlike many of those on the east coast, can be easily examined 

 from the land, when once the rocky arete linking the promontory 

 to the mainland has been passed.^ Here we find masses of various 

 shapes and sizes scattered irregularly in a sort of matrix of a reddish, 

 more or less gneissose rock. Parts of the latter exhibit a very 

 regular alternation of bands of pale, reddish quartzo-felspathic rock 

 (an ' aplite,' rather rich in felspar), and a dark hornblende- or 

 biotite-hornblende-rock, the thickness of each varying from 3" or 4" 

 downwards. In the lighter-coloured rocks a few thin, dark bands 

 may generally be seen, and in the darker a few reddish lines. 

 Sometimes the hornblende-rock is separated by veins of the aplite, 

 sometimes by a corrugated banded gneiss, as above mentioned. In 

 the lower part of the section dark gneiss, micaceous or hornblendic, 

 dominates ; higher up the pale-red aplite bands are more abundant. 

 The one rock, however, appears to pass gradually into the other. 

 That the hornblende-rock is the older, and has been brecciated by 

 the intrusion of the aplite (from which the banded gneiss cannot be 

 separated), seems to be indubitable. 



(b) Section near Port du Moulin. — On the south side of Port du 

 Moulin a natural arch ^ leads to the rocky shore, at the base of the 

 crags between this and the next recess called Saignie Bay. After 

 passing through the arch we soon come to a projecting mass of rock 



^ So explained by Mr. Hill, Quart. Journ. G-eol. Soc. vol. xliii. (1887) 

 p. 324. 



^ At one part of this a little care is required, and an inexperienced climber 

 might get into difficulties. 



3 This is dry only at half tides. It must be remembered that the rise is 

 rapid and the cliffs between the two bays are probably inaccessible. At high 

 water the waves break against them. 



