68 The Geology of the Portland Promontoryy i 



greenish-white zeolites stud the surface of the lava, standing | 

 out in bold relief Streams of hard water leak out at the | 

 junction of the two formations. These have coated much of ] 

 the lava with a crust of slippery magnesian travertine. Its j 

 colour varies between shades of dirty brown and dirty green, 1 

 but these tints may be due to the growth of microscopic i 

 plants on the moistened surfaces. Every pool in the upper i 

 rocks has a margin of lime crystals, due to the evaporation ; 

 of this hard water. As the water drips from the limestone 

 cornice it forms stalactites, the white forms of which, being i 

 relieved by the shadow cast behind them by the deep ledge, . 

 stand out as a rude dog-tooth moulding along the junction. ! 

 (See sketch V.) The step-like profile of the cliff indicates a j 

 change in the sea level. Volcanic rock appears to underlie ; 

 the whole of this cape. It dips under limestone in Bridge- i 

 water as in Nelson Bay, but what its northerly extension 

 under the limestone may be, it is impossible to sa}^ 



The third occurrence of volcanic rocks within this area is 

 at Cape Bridge water. The dunes end, and bold hills begin, 

 at the west end of Bridgewater Bay, half way between 

 Vance's and McKinlay's. At the point where the fishermen's 

 undercliff road starts, smooth wave-worn tabular rocks peep 

 up through the sand of a wide beach, between the high and 

 low water marks. These are stratified ash beds of a buff 

 colour, but they are speckled with minute black cinders. 

 The layers are each from one to four inches thick, and the 

 tint of each is proportioned to the abundance of the cinders. 

 On the beach one hundred yards south of these ash beds 

 other smoothed rocks crop up, but they are composed of a 

 dark hard lava. Immediately beyond these rocks, beds 

 of both ash and lava are to be seen in the face of the cliff! 

 The ash here is intensely hard, and is very massively bedded. 

 The colour of the upper part is buff, and that of the lower is 

 brown, and the upper edge of the brown bed forms a 

 syncline. The dip of the beds ^'aries both in angle and 

 direction within short distances. The angle of those first 

 seen does not exceed ten degrees, and their dip is north- 

 east ; but near McKinlay's (half a mile further south) the 

 dip is first east, then east south-east, while their angle has 

 risen to 40°. The ash begins to contain larger scoria as 

 we go south, and these have their vesicles filled with 

 amygdules. The upper edge of the ash is some 25 feet above 

 the beach, and the upper part of the bold cliff is composed 

 of the false-bedded limestone, first noticed at Cape Nelson. 



