GEOLOGY AND MINERALOGY. 
61 
the unstratified and the stratified formations. The Barn itself is 
a long, huge pile of alternating strata of mud, debris, and lavas, 
similar to what has been already described, rising almost perpen- 
dicularly to 2000 feet; the strata inclining 20° to the eastward, and 
35° to the northward. Passing along in front of Longwood, over 
Dead wood and Rupert’s Yalley, to the ridge which separates the 
latter from James’ Valley, the upheaval is plainly recognised at a 
point situated some little distance north of Sampson’s Battery, by 
the sudden change in the inclination of the strata from about 6° to 
b°, or 10°, and the presence of two very felspathic dikes, each 
fifteen or twenty feet in thickness, which intersect the ridge in a 
south-westerly direction ; one of these dikes, the material of which 
may be fused at no very high temperature into a kind of coarse 
Hack glass, can be traced across James’ Yalley, passing above the 
Military Hospital, and up the eastern side of the plateau which 
supports the hill called High Knoll, a lateral volcanic cone 
formed by lavas ejected through the fissure which this disturbing 
force had caused. This cone has a height of its own of about 500 
feet, while its entire altitude above the sea is 1903 feet. It is com- 
posed of very frothy, scummy lavas, tufas passing into breccias or 
pudding-stones, mixed with ashes and cinders. None of the 
lavas are compact, but sufficiently close in texture to form a good 
building-stone easily worked with the chisel, hence “ High Knoll 
stone” is much in request for the best style of building, including 
the fortifications and other military works. Most of the lava is 
however very scoriaceous, resembling a coarse kind of pumice- 
stone, and bearing more l’ecent marks of fire than any other rock 
in the Island. The formation of the cone exhibits in a most 
interesting and striking way the influence of the wind upon ejected 
matter from a volcano. That side which immediately faces the 
south-east trade wind is quite perpendicular, while the whole of the 
ejected matter has been blown in the opposite direction and built 
up three sides of a most complete cone, with its slopes inclined 
at angles of about 20° or 25°. It is remarkable that the decomposi- 
tion of this High Knoll lava produces an ashy kind of soil, in 
which few plants will grow and scarcely any thrive. Upon the top 
of this cone 1 picked up what appeared to be a lava internal cast of 
a bivalve shell, about six inches in length, and very much resembling 
unio sheppardianus, or some similar species. It is quite possible that 
