^ the Rocks of Shetland. 
sits, I have, on the contrary, been rather disposed to compare 
strata to certain crystalline laminae, which variously attach them- 
selves by their edges to the sides of nuclei. Adopting this 
view, we are then entitled to expect that strata attached to cer- 
tain sides of the claystone-porphyry as to nuclei, will not al- 
ways preserve in their connection one uniform horizontal or in- 
clined position : On the contrary, agreeably to the appearances 
presented at Papa Stour, strata of various dimensions and thick- 
ness will often meet the rocks, affording attachment to their 
edges, in every imaginable circumstance of variation and dis- 
order. 
I shall now commence my examination of the strata of Papa 
Stour at the most southerly part of the island, which is east of 
Hamna Voe, at the Point of Bragaster. Here a large mass of 
claystone-porphyry is distinctly observed to come in contact 
with a surface formed by the superior edges or outgoings of 
strata of sandstone. And since these strata contain no frag- 
ments of other rocks, being, with . the exception of their very 
red colour, similar to the rock of the same name at Sandness, I 
was inclined to suspect that many, or perhaps the whole, of 
the masses of claystone-porphyry might be superimposed on a 
surface of sandstone. But, on the contrary, there is no evi- 
dence to shew, that the part in contact with the sandstone may 
not belong to the deep impendent side rather than to the under 
surface of the porphyritic mass ; consequently, the relations of 
the under surface of the unstratified rock may be perfectly un- 
known : Or, again, that part of the porphyry in contact with 
the sandstone, may belong to a small portion only of the under 
surface of the superimposed mass. The rest of the under sur- 
face may be in contact with rocks of a very different descrip- 
tion. Thus, the Voe Skerries lying to the north-west of Papa 
Stour, and the rocks of Norbie, situated to the south-east, are 
all composed of hornblendic gneiss; and when we take into 
consideration the detached fragments of hornblende, and slaty 
actynolite, abundantly found in the island, either a part or the 
whole of the rocks of Papa Stour may, for any thing that can 
be proved to the contrary, rest upon a surface formed by the 
outgoings or upper edges of strata composed of hornblendic 
gneiss. 
VOL. II. NO. 4 . APRIL 1820 , Q 
