XORTII-WEST REGION (JF CUARNAVOOD FOREST. 85 



now viridite, but siia;g'estivc of having Loen a glass. The quartzes, 

 though fewer and smaller, arc like those of Sharpie}' and. Peldar : 

 (here are the occasional small clusters of epidote and the composite 

 grains, darkened with opacite. The slide includes at one edge a 

 small portion of a felted mass of small plagioclastic felspars with a 

 little epidote and black iron oxide, whicli recalls the structure of 

 the fragments included in the Peldar rock, and the matrix now 

 resembles that of the latter, now that of the Sharpley rock — the two 

 being rather " streaked " together, as if a sliglit fiuidal structure 

 were present. The mode of occurrence and aspect of this rock in 

 the field suggests that it is a dyke,, and this view accords fairly with 

 the microscopic structure. If so, it confirms our present interpre- 

 tation of the typical Sharpley and Peldar rock. It is, we may add, 

 the only case in which field evidence strongly suggested the presence 

 of a dyke in this region, and this is certainly remarkable, seeing 

 that agglomerates and ashes are so abundant. 



The outcrop called the Swanymote liock*, at the north-western 

 extremitj' of the Sharpley massifs presents considerable difficulties. 

 The mass may be roughly divided by a line running from rather IS. 

 of N.W. to rather 8. of S.E. The portion on the eastern side con- 

 tains fragments of a dull-purple porpbyritic rock, like that often 

 seen in the neighbouring agglomerates. In that on the western 

 side it is doubtful whether any of these fragments are present, but 

 pieces of slate, sometimes quite 2 feet long, occur, generally green in 

 colour, but in a few instances purple. Once or twice they are distinctly 

 banded, and thej have been bent, but the bending was apparently 

 anterior to the production of a cleavage in the matrix, which has 

 hardly produced any effect on them. The matrix of the massif 

 is rather irregular in structure — quartzes and felspars abound. The 

 rock sometimes appears identical with the normal porphyroid of 

 Sharpley, but occasionally is more suggestive of a pyroclastic origin. 

 An adjoining knoll, to the W., in parts resembles the purple por- 

 pbyritic rock just described as occurring in fragments, but in others 

 contains numerous and large quartzes, and exhibits in its purple 

 groundmass a curious mottling of a light grey colour, which is 

 suggestive of a flow-brecciatioii. Possibly we may be here just on 

 the edge of the lava-flow, and the mass may be more or less a true 

 pyroclastic rock. The outcrops between the Swanymote Eock 

 and Cademan Wood are fairly compact ashy grits, one of which 

 contains occasional quartzes and felspars. 



One feature of these volcanic materials, whether lavas, agglome- 

 rates, or tuffs, is rather remarkable. This is the absence in the 

 larger masses of any very determinate characters. In those now 

 considered to be lavas, the lath-like microliths, so common in ordi- 

 nary trachj-tes, ate never more than very imperfectly seen, and 

 they are often wholly wanting. Fiuidal, perlitic, and spherulitic 

 structures ha\e not yet been found. In the fragments in the agglo- 



* Referred to in former papers as beiug " near the last letter of the word 

 Swanymote " on the one-inch map. 



