SAEK, HEEM, AND JETH0TJ. 



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grains of 0*1 or 02 in eh in diameter, which often aggregate together, 

 glassy qnartz of like size, and black or dark green hornblende. The 

 microscope adds to these sphene and apatite. In colour and degree 

 of coarseness it is not unlike some Leicestershire syenites from the 

 Enderby and Sapcote group. Thus it might be called a granite, 

 but for its very decided structure, which is visible even in hand- 

 specimens as a parallelism of the grains and a tendency in the 

 felspar to aggregate along parallel surfaces. In the lower part of 

 the cliff this is especially conspicuous ; for the structure weathers 

 out into well-marked lines which indicate a dip of 30° in a N.W. 

 direction. We may thus designate our subject of investigation a 

 syenitic gneiss with a rather rude foliation. The rock passes out to 

 sea, and appears to constitute the Burons, the Grand Moie, and 

 possibly other isolated rocks. Southwards from the harbour it 

 furnishes the face of the cliffs up to within a few feet from their 

 crest all the way to Point Terrible, where it ceases abruptly. 

 Northward it forms the base of the cliffs for a short distance, but 

 sinks entirely out of sight some distance before Point Robert. Thus 

 practically it can be examined only at the harbour ; in a walk along 

 the cliffs the foot treads nothing but schists ; and as the appearances 

 of dip differ little, I do not wonder that many visits had been paid 

 to the island by others and by myself before the discovery was 

 made that here is a new and different series. 



Fig. 3. — Hornblende-schists overlying Gneiss, seen across a cleft 

 in iJie Cliff north o f Point Terrible. 



The relations between this gneiss and the overlying schists are not 

 altogether easy to establish. The junctions, though fully exposed, 

 are all nearly or quite inaccessible. By passing along the cliff edge and 

 venturing down some rather steep grass slopes a very near view can 

 be obtained across clefts (fig. 3), and the harbour cliffs give an ex- 

 cellent section (fig. 4). The dip of the gneiss is exactly JST-.W., while 

 that of the schists, so far as it can be estimated, is rather more nearly 

 W. The passage from the one to the other is everywhere abrupt 

 and definite to the eye. The highly quartzose gneiss must have had 

 a very different origin from the quartzless hornblendic rocks. The 

 nature and thickness of the immediately overlying beds seem to vary 

 at different spots ; and those in actual contact with the inferior 



