900 T. G. BONNEY ON TUE SERPENTINA AND 



schistose structure. The top aud bottom of the rock shows the usual 

 mineral changes. The serpentine in contact is much cracked and 

 burnt. The projection of rock, which forms the western limit of the 

 port is cut by a dyke of newer gabbro ; aud the same rock, a few 

 yards further on, appears at the base of the cliff on which the village 

 stands ; an isolated patch also breaks through the serpentine on the 

 shore. A few yards from this is the first patch of the older gabbro. 

 This older gabbro forms the base of the cliff for a short distance, 

 while the shore consists mainly of newer gabbro, veins of which cut 

 the older. Just where a projecting angle of the cliff begins is an 

 interesting junction. The older gabbro is cut by a dyke of newer 

 gabbro about 18 inches wide, and both again cut by a dark trap dyke 

 about 12 inches wide (fig. G). The two intrusive dykes are displaced 

 by a fault of a few inches. This last dyke (1) may be traced for 

 some distance towards the sea ; its general direction is N.N.E.-S.S. W. 

 At the angle named above, serpentine replaces the newer gabbro, 

 both on the shore and in the cliff, and on the whole is continued to 

 beyond another small projection. 



Here another trap dyke (2), generally about 5 inches wide, 

 may be traced about 20 yards along the shore in a northerly 

 direction. Beyond this veins of the newer gabbro break repeatedly 

 through the serpentine. Then comes a dyke of compact trap (3), about 

 4 inches wide, cutting into the cliff and running N.N.W.-S.S.E. 

 Beyond we find serpentine with intrusions of newer gabbro, till we 

 again find the older gabbro beneath the cliff, broken into by the 

 newer, and both cut by another compact trap dyke about 1 foot wide. 

 A few yards further, over serpentine and newer gabbro, is another 

 trap dyke cutting both, exposed up the face of the cliff for 7 or 8 feet. 

 It is about 3 feet wide, and rather coarser in texture than the others. 

 Well-marked horizontal joints give it a slightly columnar aspect. 

 The shore for some little distance further consists of serpentine with 

 some intrusive newer gabbro, and at least one more dyke of com- 

 pact trap. 



It will now be convenient to describe more precisely the litho- 

 logical characteristics of these rocks, omitting at present the serpen- 

 tine. 



The Older Gabbro. — This might easily be mistaken for a mere 

 variety of serpentine *. It has a compact, dark, dull red or purple 

 groundmass, often mottled with a brighter red, in which are im- 

 bedded crystalline grains of a greyish white felspar, perhaps about 

 0*2 inch in diameter, and some rather smaller crystals of diallage, 

 generally about \ to | inch apart. The matrix for a quarter of an 

 inch square or more is often unbroken by any crystals visible to the 

 eye ; occasionally, however, the felspar predominates. The rock 

 does not vary much in texture, the smaller veins being about as 

 coarse as the larger masses. One small boss has the groundmass a 

 dark green instead of red. It is, however, the same rock, though 

 as a rule it is rather more finely crystallized than the average of the 



* As it is described by most writers who have noticed it. 



