at Portland Bay. 171 



encrust it with a thick coating of stalagmite. Huge boulders 

 lie at the foot of the cliffs. They are water- worn and very 

 vesicular. It is not, however, at all decomposed, and the only 

 effect time has had upon it is to fill every available crevice 

 with lime. In fact, it is an amygdaloidal lava. A small 

 fragment of this infiltrated trap looks precisely as if it were 

 studied with lentils of wax. Some of the larger vesicles 

 contain very red acicular crystals of carbonate of lime, radiat- 

 ing from the centre towards the circumference. There can 

 be no doubt it has flowed under the sea, aud the huge hills 

 and valleys which it seems to have covered, show that the 

 bottom could not have been very level at that time. As the 

 coral strata must have been deposited while the bottom was 

 subsiding, the volcanic disturbance most likely created a 

 change, and gave rise to elevation. This explains why no 

 coralline is found above the trap ; for the same effect which 

 caused it to be covered, rendered the surrounding circum- 

 stances no longer favorable to its growth. 



Immediately above the trap occurs the crag. This has 

 been already described ; but there is a reason why it should 

 be slightly dwelt upon now. In the first place, it shows very 

 clearly that the lava was not of sub-aerial origin, these strata 

 having been formed under the sea. The strata, properly 

 speaking, are about twelve feet thick, and are much con- 

 torted. This is not from the manner in which they have been 

 upheaved, for no two strata correspond. The lower ones 

 are sometimes horizontal, while those immediately above 

 are waved and undulating. Between these great divisions of 

 the strata there are cross laminations dipping in every direc- 

 tion. All these facts, and the nature of the stone, which is 

 composed of calcareous sandstone, shows that the deposit was 

 formed by a deep-sea current. As on each side of Cape 

 Grant there are rises of trap rock, the thickness of the beds 

 may be due to a valley in the sea bottom, in which sediment 

 would more easily collect. The crag here, as at Guichen 

 Bay, contains the root like concretions. They are termed 

 roots, and so great is their resemblance to the name they 

 bear, that it is extremely difficult at first to explain their 

 purely aqueous origin. Darwin mentions a similar appear- 

 ance on the Bald Head in Western Australia. He considers 

 . them in that place to be really vegetable casts. He supposes 

 sand to have drifted round bushes and trees, and subsequently 

 consolidated, and when the wood decayed away, the hollows 

 became filled up by infiltered lime, which being harder than 



