56 
ST. HELENA. 
and plionolite. This order of succession is repeated several times, 
the occurrence of the layers of heavy blue basalt, with em- 
bedded crystals as before mentioned, being at altitudes of 200, 
300, and 400 feet above the sea line, until the whole Island is built 
up to the crater’s edge.* While some of the lava beds are very 
compact, others are more or less scoriaceous and cellular,! their elon- 
gated almond-shaped cavities clearly indicating the direction of their 
flow. In addition to this evidence, and that of the angles of incli- 
nation, that the strata have scarcely been disturbed from their 
original positions, when flowing from Sandy Bay northward, we also 
find the embedded crystals of augite, one of the most brittle of 
minerals, to exist in a perfect state only around the neighbourhood 
of Sandy Bay. All the embedded augite, on the northern side of 
the Island, has been broken into small irregular fragments, evi- 
dently by attrition while flowing to so great a distance. Scarcely is a 
complete crystal of this mineral to be found beyond the walls of the 
crater, while inside the crater itself, as at Lot and other places, the 
most perfect crystals exist in large numbers. 
It is somewhat remarkable that, excepting the beds of hard 
basalt containing embedded crystals, the lavas show a gradual ten- 
dency to a more felspathic composition as they approach the highest 
part of the Island ; the most recent being also the most felspathic. 
Lavas of such a character are more readily acted on by atmospheric 
influences, and, being more easily reduced by disintegration into 
alluvial soil, seem to indicate a thoughtful care on the part of the 
Great Creator, in thus facilitating the process for forming a surface 
soil to this rocky land. Still more strikingly is this illustrated by 
the fact that all the uppermost layers of lava which once existed, and 
have now through disintegration entirely worn away from the high 
central parts of the Island, had felspar for their chief constituent. 
* These Basaltic layers are seen cropping out on Munden’s Point and Hill ; they appear 
also at the following places : above Chubb’s Spring House, immediately over the bridge and 
little waterfall at the foot of Barnes’ Road, about half way up Barnes’ Road, at Francis Plain 
and along the watercourse road, and also at Southerns, where a thick flow on the roadside is 
most probably the same as that seen at Francis Plain ; ,l The Rock ” in Plantation grounds, 
as well as a stratum at Arnos Vale entrance iron gates, show the same composition; while im- 
mediately over Cat Hole there occurs a layer of greystone with only a few small widely 
scattered crystals of olivine. It is not these but the pure basaltic lavas which generally follow 
on the beds of laterite. 
t Towards the lower part of Barnes’ Road a layer of very cellular lava, with cavities about 
the size of peas lined with very minute zeolitic crystals, occurs. 
