Dr Hlbbert on the Distribution 
ed, as we trace it from the south, a mass of sandstone or granu- 
lar quartz, the eastern boundary of which may be traced from 
its junction with the red quartz of the Hill of Walls, along the 
coast as far as the House of Melby and to the Holm of Sand- 
ness. The sandstone differs from tlie red quartz, by containing 
less felspar, by possessing a structure more granular and less 
hard, and by the general whiteness of its colour. The direc- _ 
tion of the strata is generally about N. 55® E., the dip being 
to the east under an angle of 45® ; frequently, however, a 
much less inclination is observable. Near Eastgio, the sand- 
stone is associated with strata of clay-slate, almost horizontal, 
and, near the House of Melby, with claystone porphyry of a con- 
glomerate structure. 
As we approach the shores of Papa Stour, the sandstone 
ceasing to become the prevalent rock, we observe the island to 
be chiefly composed of felspar-porphyry. This rock admits of 
several varieties. Of these, the first is found chiefly on the 
south-east of the island near North-house : it contains a great 
excess of felspar, but is slightly porphyritic ; the colour of the 
rock is brick-red. The second variety, occurring on the north 
and north-east, also occasionally on the south of the island, 
is denoted by a greater quantity of argillaceous matter, 
which being of a deep reddish-brown colour, and unequally 
combined wdth red and reddish-white felspar, often gives the 
rock a variegated appearance. The third variety differs little 
from the other, except in being less variegated, and in the 
greater number of its crystals of felspar. It is to be found on 
the south-west and west of the island. 
‘ The claystone porphyry, which is generally, in Papa Stour, 
an unstratified rock, may, in reference to the varieties which it 
exhibits, be resolvable into several distinct masses, the bounding 
sides of wdiich not coming into mutual contact, their intervening 
spaces are supplied by strata. In other instances, the strata 
appear to merely fill up those concavities of the porphyry 
which are of a subordinate depth. Rejecting, then, any mecha- 
nical notion which would refer the intervention of strata be- 
tween the rocks, or the filling up of inequalities, to the circum- 
stance of one stratum in a series regularly reposing upon ano- 
ther, as if rocks w^ere the result of a number of successive depo- 
