THE VICTORIAN NATURALIST. 163 



A nodule of quartzite, quartz grains in a ferruginous and 

 silicious matrix, appeared as if fused. Experiment showed that 

 the iron was in sufficient quantity for the matrix to fuse slightly 

 and become magnetic before the blowpipe. 



The tuffs are distinctly stratified, but with many irregu- 

 larities. The thickness of any individual bed varies very 

 much, apart from the effect of a large block in it. False 

 bedding is prevalent. At one place a hollow of some size 

 has been made in the lower beds prior to the deposition of 

 the upper ones, and these thicken into the hollow, crossing 

 the edges of the lower ones at the sides. A fracture appar- 

 ently prior .to the formation of the upper beds was noticed at 

 one place. Where a block has fallen the beds below are more 

 or less dented or broken. Under small blocks there is usually 

 only a slight bending, but the larger ones often penetrate the 

 beds below, curving and fracturing them. Several of the largest 

 blocks are found to belong to one time, being contemporaneous 

 with a bed containing a number of blocks of basalt and granite, 

 but they themselves now occupy a position below it. A block of 

 basalt of 4 feet horizontally and about 3 feet deep has its upper 

 edge about 3 feet below the bed, and is seen to have cut through 

 the beds, the broken ends being about 10 feet apart at the edge 

 of the hole it formed. A block of granite about 2 feet thick and 

 nearly 6 feet high stands with its upper edge in the same bed. 

 Its sides are flat, representing two parallel joint planes of the 

 granite. The block before mentioned as the largest seen in the 

 cliffs occupies a similar position. It is soon seen that size is 

 not the only factor which influences the depth of penetration. 

 Evidently velocity, which depends on the height from which it 

 has fallen — that is, on the force of ejection— must affect it, and 

 also the shape of the block, and especially of the part which first 

 strikes the bed. The cavities formed where a block has fallen are 

 filled in with smaller materials ejected at the same time. A very 

 large basalt block lies on the beach near the same place. It 

 measured 8 feet 6 inches by 5 feet transversely, and if some 

 neighbouring pieces were part of it, would exceed in bulk the 

 granite block referred to before. 



On the weathered surface the blocks and fragments stand out 

 but are firmly attached to the finer materials. There are no 

 loose cinder beds like those of Tower Hill. All along the cliff 

 slipping has taken place, cracks being formed parallel to the 

 cliff, by which large masses have been allowed to move. 



Sometimes there is a detached pillar of tuff. At other places 

 caves have been formed, probably largely by the influence of 

 water running in cracks. The roof of such caves sometimes 

 collapses, covering the beach with blocks of tuff. Basalt and 

 granite blocks occur all along the beach, weathered out from the 



