226 GENERAL GEOLOGY 



thus not only masking the face of the cliff, but also making the upper portions of 

 the exposures very difficult of access. 



The section of the cliff is roughly as follows : — 



A. The northern part of the exposure consists of a kenyte flow or series of flows 

 of considerable thickness. The kenyte is of a very different appearance from that 

 which forms Cape Royds and the Skuary, but one which is quite common amongst 

 the erratics at Cape Royds. The felspars are in shape very flattened and plate- 

 like, arranged with an orientation usually parallel to the direction of the dip of the 

 flows, but occasionally arranged in a way which gives a very beautiful curvilinear 

 flow structure to the rock. The ground mass is stony and reddish. It is impossible 

 to gauge the thickness of the flow, as to the north the whole of the surface is covered 

 by a magnificent ice-cascade, so that the next exposure north of the Turk's Head is 

 the Skuary, consisting of a different type of kenyte altogether. This kenyte of the 

 Turk's Head and all the other rocks of the exposure dip to the north-west at an 

 angle of about 45°. 



B. To the south of the kenyte a very coarse agglomerate sets in. Tlie boulders 

 comprising this agglomerate, many of them 18 inches or 2 feet in diameter, are 

 usually spherical in shape, with a concentric orientation of the felspars, and this 

 appearance was much accentuated in those blocks which had been exposed to sub- 

 aerial denudation for a considerable time by a concentric type of weathering. This 

 resulted in a series of different rings, varying from brown on the outside, where the 

 iron salt had been converted into limonite, through red to the natural black of the 

 rock. The blocks examined seemed to be of a fairly even texture throughout, but, 

 despite this absence of the vesicular bomb-structure, the fragments must have been 

 ejected from the crater in a semi-molten state, for a high degree of jilasticity would 

 be necessary to account for the very perfect orientation of the phenocrysts. If this is 

 the method of formation of these blocks, this particular portion of the lava must have 

 been remarkably free from occluded water. 



The ground mass consists of an aggregate of fragments of volcanic glass, small 

 fragments of the local kenyte with platy felspars, fragments of felspars, and of fine- 

 grained brown cement. 



C This bomb agglomerate is succeeded by a flow of kenyte of the same type as 

 the last about 20 feet thick, and this again is succeeded by, 



D. Bed after bed of tuffs, some of fine material, showing bedding planes, and 

 others of coarse boulders, with less of fine cement, appearing quite massive, and 

 with no visible evidence of stratification. 



Material of every size is present in this series of beds, from the massive boulder 

 to the finest dust, and the alternation of these types has given rise at the southern 

 end of the exposure to a splendid series of crags and pinnacles exactly like the spires 

 of a cathedral, and the picturesque effect is much heightened by the way the 

 weathered fragments stand out like great bosses from the tuff-like cement. 



