QQ The Geology of the Portland Fo^omontory. 



In places the lava lies immediately upon the miocene 

 shell bed, but I did not detect any changes in the latter, 

 such as are usually caused by contact with heated masses. 



I was much struck with the great differences in colour, 

 degree of hardness, vesicularity, decomposition, and thickness 

 of bedding, displayed by the lava within short distances. 



Woods has tested the rock, and he assigns to it the 

 following composition : — 



Si.02 ... ... ... -60 



Fe. O -20 



AI2O3 ... ... ... -10 



Ca. 0. ) 



Mg. 0. Y ... ... ... 10 



H,0. j 



100 



He terms it an augitic or doleritic lava, and it seems to 

 me that it might equally well be called an andesite. 



A fine grained yellow, slightly vesicular and very decom- 

 posed lava occurs in a little bay immediately south of the 

 hghthouse. It is found at, and a little above, the low water 

 level, and its softness probably accounts for the formation of 

 the little bay. Similar flows occur at the sea level in all the 

 indentations between this bay and Danger Point, and I 

 noticed that wherever the coast juts out the rock at the sea 

 level is a dark durable lava. The yellow lava appeared to 

 me to be of a more acid nature than the darker kinds, for it 

 preserves its light colour even where it is very hard and 

 undecomposed. At Black Nose Point the rock is a dark 

 massive hard basalt, and it is so very vesicular that a gas 

 cavity, which I measured, had a major axis 18 inches long 

 and a minor one measuring 1 2 inches ; and I saw many 

 others as large as it. A tiny rivulet enters the sea near to 

 this point, and thereabouts the clifls lose their height, and 

 then the coast forms a low double shelf (See Sketch K.) 

 A pebble ridge extends from this place to Danger Point, 

 a distance of one mile. The boulders are of basalt, with an 

 abundant admixture of rolled blocks of volcanic ash, and 

 flints. The ash may come from the Laurence Rocks, one 

 mile to seaward of the ridge ; but if it does not, it is hard to 

 say whence it is derived, as there is no other deposit of the 

 material, known to me, nearer to it than Cape Bridge water, 

 which must be 15 miles distant. This volcanic formation 



