716 Proceedings of the Royal Irish Academy. 
A primary and universal shearing is not found in the normal "Old 
Boy" of Sutherland, E-oss, and Cromarty; for in the space of a few 
yards the direction of the strike may change two or more times, while 
the dip is so variable that to me it appeared that the foliation could 
not have been generated by a shearing force coming in one direction, 
as is stated ; but that it was induced by previous structures. If so, 
each change in the direction of the strihes and dips suggests different origi- 
nal beds of rods, and not ati uniform origin, due to the tearing up of a 
mass of intruded roch. 
From what I have learned elsewhere, in metamorphic and sub- 
metamorphic territories, I am convinced that the general metamorphics 
of the "Old Boy" of Sutherland, Boss, and Cromarty, took place at 
one and the same time ; that is, that the general metamorphosis of the 
Couuty Bocks and of the associated dykes was simultaneous ; the 
foliation in the first being induced by their different prominent 
structures, and those in the dykes by theirs. This seems to be 
ocularly proved, especially in the latter, where the foliation has all 
the variations that will be found in the structure of unaltered dykes. 
As to the County Bocks, I will not hereafter be surprised to hear that 
on the surface of some of the quartzites elongated ripple-marks will 
be found, as in my hurried visit I saw marks very like such. 
We were also shown dykes that are of greater or less width when 
crossing the County Bocks, but that lessen considerably in the fault 
lines {upthrusts) ; this lessening being said to be due to their being 
drawn out by the thrusting along the faults. Possibly this may 
be the case ; but as a general rule, dykes crossing strata a/re better 
developed than when running along it, or along lines of fault. This 
can be seen in connexion with the dolorite dykes in the Carbo- 
niferous slate of county Cork, and the dolorite dykes in the metamorphic 
and granitic rocks of Galway, Mayo, Donegal, &c., their make being 
very similar to that of a metalliferous vein, which are usually well- 
developed lodes when crossing the County Bocks, while they may be 
mere leads when the veins take to follow the bedding. 
In connexion with the dykes, it may be mentioned that we were 
shown "whin sills" that were said to be " undoubted intrusive sheets." 
Curiously, however, each had its own special geological horizon ; and 
of shale, sandstone, and limestone, so that now the different classes of rock, although 
very little altered, are very conspicuously interlaced — sometimes this is on a large 
scale ; on a small scale it can be seen in a limestone quarry at Kiltoy, N. E. of 
Letterkenny. 
