Geology. 285 



southern end of this coast, a little north of Eoss Hill, I found basalt 

 pebbles up to 400 feet. 



In the neighbourhood of the fresh-water stream are some rounded 

 knolls, and in a shallow valley between these 1 found an exposure 

 of a trachytic rock similar to that described from Flying Fish Cove. 

 This exposure was of small extent, and seemed to be completely 

 surrounded by basalt, of which the knolls are composed ; the 

 relations of the two could not be made out, the ground being for 

 the most part covered with a dense jungle of screw-pines, veiy 

 difficult to penetrate. The basalt at this point forms a great part 

 of the shore terrace, and appears on the shore in the waterfall 

 bay and in another bay a little to the south. At the stream it is 

 covered by thick beds of red palagonite tuffs, and it is to the 

 presence of these volcanic rocks that the existence of the two or 

 three small brooks is due. The palagonite tuffs are covered with 

 coral limestones, the age of which is not known. At the waterfall 

 (Panchoran Bay) the basalt fonns an extensive sea- worn platfoiTu 

 (Fig. 9), and on the beach forms a projecting ledge over which 

 a pei'enuial stream of excellent water flows. The basalt at this 

 point, which is near the centre of the mass, contains porphyritic 

 crystals of felspar, augite, and olivine. There seem to be two 

 kinds of porphyritic felspars, one in well-defined twinned crystals, 

 probably labradorite, the other less well-defined and with distinct 

 zonal banding ; this is probably more acid. The olivine is usually 

 altered into a pleochroic fibrous serpentinous mineral. Ground-mass 

 of microliths of felspars, augite, and magnetite. Above the basalt 

 at this point is a bed of volcanic conglomerate, consisting of blocks 

 of basic rock, some vesicular, some compact and glassy, mostly 

 more or less rounded ; these are embedded in a ground-mass of red 

 volcanic ash with much lime ; in fact, at the top of the bed the 

 pebbles of basaltic rock are embedded in hard limestone. The 

 greatest thickness of this bed measured was about 1 feet. Upon 

 it is a bed of hard yellow limestone, the age of which is doubtful. 

 The absence of Orhitoides (see iS'o. 52, p. 259) is against its 

 Miocene age, but on the other hand Dr. Gregoiy has doubtfully 

 referred a coral from this bed to a species ( Orbicella murrayi^ 

 p. 216) found elsewhere in the Orbitoidal limestone. Upon it 

 is a thick mass of limestone breccia, the blocks composing which 

 are of all sizes and cemented by finer mateiial, often filled with 

 phosphatic nodules ; probably the whole is a submarine talus of 

 comparatively recent date derived from the cliffs behind. This 

 is capped in turn by a reef-limestone of quite recent date (probably 

 late Pleistocene). The cliff at the north and south of this bay 

 is therefore formed (from below up) by (1) basalt, (2) volcanic 

 agglomerate, (3) yellow limestone (4 or 5 feet), perhaps of 

 Miocenea ge, (4) limestone breccia, an old talus, (5) late reef- 

 limestone with corals like those now living on the coast. 



A few hundred yards farther south the sea-washed platform 

 is composed of a basalt of a very different character from that 



