GEOLOGY AND MINERALOGY. 
51 
upon which it stands. A mile further on, in the same direction, 
stands a third of these columnar remains, called the Ass’s Ears ; and 
still farther on for about another mile, rising as an islet from the 
sea, detached from the main land, is seen Speery Eock, the last 
visible portion of this great dike. 
There is no difficulty in tracing the relationship of these rocks 
as portions of the same great dike, because in character and com- 
position they agree exactly, while the rocks which enclose them are 
of a very different construction, consisting for the most part of 
unstratified blue basaltic, hard- red, and other marls, containing 
embedded crystals of augite, and traversed in all directions by 
numerous very small dikes. These features are so intimately 
associated with the great crater of Sandy Bay that it is difficult to 
omit noticing them in connexion therewith ; but, in tracing out the 
geological structure of the Island in due order, their introduction at 
this point is somewhat out of place, as will be understood when it is 
remembered that they were certainly formed after, perhaps long 
aftei, the great volcano had ceased to be active ; and as yet we have 
not seen what became of the products cast outside of the crater- 
vvalls during its activity. 
With the intention, then, of returning to this subject in con- 
nexion with the denudation and probable age of the Island, let us take 
a y iew of what surrounds the great crater edge, or Sandy Bay Eidge, 
°n its northern, eastern, and western sides — in other words, the 
great masses of lavas, ashes, and mud, which, ejected from the crater, 
have built up the remaining portions of the Island. 
We find no trace whatever of granite or any other primitive or 
Plutonic rocks, or indeed any formation to encourage the slightest 
suspicion of a continental land having ever occupied that particular 
latitude and longitude where St. Helena now stands. Continental 
land may at some extremely remote period have occupied the same 
place, but, be this as it may, there can be little doubt that, previous 
to the appearance of St. Helena, the broad expansive South Atlantic 
swept over the site it occupies ; and the first sign of disturbance 
there was probably a bubbling and spouting up of the water on a 
vast scale, just at or near to the spot now called Sandy Bay Beach. 
Then followed a stream of molten lava, shot up from the depths of 
the ocean, and, guided by the south-east wind, falling into it again 
more on one side than the other, laid the foundations of that pile, 
e 2 
