soo 
Dr Hibbert on the Distribution 
expressing every condition of strata. Where strata are observ- 
ed to have a lateral attachment to each other, or where the 
lines of bearing denote uniformity, it may perhaps be jus- 
tifiable, in describing such strata, to use the word Collateral, 
This expression of collateral strata,, will apply to many circum- 
stances where strata are not of equal thickness, or where they 
occasionally become indistinct, from a transition into each other 
at their sides, or where, added to this circumstance, they are so 
curved or bent out of their course, as that their lines of bearing 
shall occasionally vary several degrees. . 
When, however, collateral strata, if I may be allowed to 
adopt the expression, are of uniform thickness, and are uninter- 
rupted in their course, we may then properly enough distin- 
guish them farther by the name of Pai'allel strata. 
The inclination of the strata of Fitful Head, is with dillicuity 
estimated, owing to circumstances already stated, namely, their 
distorted state, and their lateral transition into each other. The 
dip is generally to the east, at an angle of about 40°. 
In the mica-slate, about a mile to the west of Quendal, is 
a thin mass of limestone, the strata of which run east to west, 
in a direction strictly unconformahle to that of the adjoining 
strata : that is, the lateral edges of the mica-slate are opposed 
to the lateral planes of the limestone. Here is a slight exempli- 
fication of the distinction which I have maintained as subsisting 
in the relations of strata, and tending to justify the use of the 
term collateral strata, as applicable to the mica-slate. 
At Garthsness, near Fitful Head, in the mica-slate, occurs a vein 
or perhaps bed of iron-pyrites, running nearly north and south, 
which was a few years ago unsuccessfully wrought, for the purpose 
of finding copper-ore, whilstmany hundred tons of iron-pyrites were 
thrown into the sea. The site of the ore is so much concealed 
by the fragments thrown up from the mine, that its breadth is 
not very distinct^. I observed four and a half feet in width, of what 
the Cornish miners, who worked here, called Gossan, which 
consisted of pulverulent siliceous matter, mixed with iron-ore, 
and eight and a half feet of what was named by the same men 
the Rider, consisting of iron-pyrites, t;ccurr;rg in a highly in- 
* Dr Fleming’s account of these n ines of Dunrossness, in the Appendix to 
Shiirelf’s Agricultural Survey of Orkney and Shetland, may be consulted with ad» 
