136 MESSES. C. I. GARDINER & S. H. REYNOLDS [Feb. 1 898, 



II. The Sedimentary Rocks. 



At the north-western corner of the island, in Saltpan Bay, is an 

 exposnre of brown fissile slates, faulted, along its western edge, 

 against an andesite, but apparently overlain conformably to the 

 east by igneous rocks ; for though at this junction, which can be 

 seen at sea-level, near Calico Hole, the slates appear somewhat 

 crushed, the line cannot be taken as a fault. 



Exactly similar slates are to be seen in the road north of the 

 Castle, about | mile south-west of Saltpan Bay, and, though the 

 intervening country is drift-covered, it is probable that the two sets 

 of exposures are in the same bed of slate, as is suggested in the 

 Survey Memoir (p. 49). 



Similar slates are exposed in Broad Bay, the next bay to the 

 west of Saltpan Bay, and they run across the inner end of Scotch 

 Point, being seen on its western side. The ashes forming Scotch 

 Point underlie these slates conformably. 



No other sedimentary rocks are to be seen on the western coast of 

 the island, but on the south-western side, in Talbot's Bay, patches of 

 green and red slates occur, several yards in length and breadth, 

 entirely surrounded by the dark green andesite which here forms 

 the coast. In places these slates are baked by the igneous rock, 

 and at one spot they contained Orthis hiforata. Bands of grit and 

 tuff occur with the slates, the tuff-bands containing fragments 

 of grit, slate, and ash. 



The middle of Talbot's Bay is cut out in black and green slates 

 showing much contortion and containing bands of purplish grit. 

 These beds are so utterly unlike the brown slates exposed in 

 Saltpan Bay and near the Castle that we cannot fall in with the 

 suggestion in the Survey Memoir that they are ' evidently a portion 

 of the same Silurian slates.' 



The Talbot's Bay slates are, however, extremely like those 

 exposed in Carnoon Bay to the south-east, the coast between the 

 two bays being formed of a coarse tuff or agglomerate. The 

 Carnoon Bay slates are black and purple in colour, and contain 

 a tuff-band somewhat similar to that which occurs in Talbot's Bay. 

 To the south many small patches of red and green slates and 

 fine ashes are exposed, caught up in the andesite, which here forms 

 the coast-line, the smaller inclusions being baked and porcelainized, 

 the larger ones showing no signs of alteration. 



The largest and most important mass of sedimentary rocks thab 

 occurs in the island forms the summit of Heath Hill, and occupies 

 the shore-line from Kiln Point to Seal Hole. 



To the north-east these rocks are bounded by a fault, which can 

 be seen at the top of the cliff on the northern side of Seal Hole. 

 At Xiln Point, to the south, the junction is seen to be an unfaulted 

 one, the limestone overlying the igneous rock, and here the former 

 rock shows evidence of alteration by the andesite. This alteration 

 is visible both in a hand-specimen and under the microscope, the 

 limestone becoming thoroughly crystalline and the shaly partings 



