^tlie Hocks Shetland, 299 
veins of granite, to which immediately succeeds the mica-slate 
of Garthsness. More westerly ensues the large assemblage of 
strata composed of clay-slate, which forms Fitful Head. Still 
more westerly at Noss, a headland to the north-west of Fitful 
Head, occur a few strata of gneiss and mica-slate, which are 
traversed by granite. 
The stratification of the whole of this mass is confused, and, 
as far as an estimate can be made of the direction or line of bear- 
ing as it occurs at difierent places, the lateral planes of the stra- 
ta cannot be considered as parallel to each other. This un- 
conformity in point of parallelism, is observable where strata 
are not disturbed by the presence of traversing masses of lime- 
stone or granite, as in the clay-slate of Fitful Head. The stra- 
ta are constantly observed to pass into each other laterally, or to 
be united by their sides, the tabular seams by which they were 
separated becoming evanescent ; nor can any stratum be traced 
far, before it is thus observed to be lost, whilst new tabular 
seams are in equal number appearing at the same time in other 
places. The strata are also often curved or bent out of 
their course. Still the direction assumed by the strata may be 
generally stated at 15° north of east, variations from that point 
of the compass occurring to the amount of 15° or 20°. 
It is worthy of general remark, that circumstances of stratifica- 
tion like these are so constantly appearing, as to render extremely 
vague the idea of cmformity^ which has been often deemed only 
applicable to strata, where there is a parallelism of their lateral 
planes. It is always inconvenient to forego terms that are in com- 
mon use, but if the term conformityi^ still to be used in speaking of 
strata, it would perhaps be better that the word should be restrict- 
ed to those circumstances where strata are found to have no other 
relation to each other at their junction than one that is lateral; 
for it is worthy of particular notice, that two stratified rocks are 
often found so to vary in the direction of their respective strata, 
that where the contact takes place, the sides of one set of strata 
are opposed to the lateral edges of another set. Here, then, 
I conceive, is a good ground for the distinction of rocks 
into conformable or unconformahle. But, at the same time, I 
would submit, that much more descriptive words, and not liable 
to such ambiguity, may be found, which might be capable of 
