296 REV. J. F. BLAKE ON A REMARKABLE INLIER  [ May 1902, 
talus, fault-rock, or whatever we may choose to call it, is seen to. 
go to the top of the waterfall and to continue to the base, making 
the surface irregular throughout. | 
We are here able to trace continuously the Jurassic rocks to their 
junction with the Caithness Flags, and to see them apparently 
passing into the fragments of the latter, just as we might trace the 
mud of a sea-bottom passing by stages into the débris which has. 
accumulated at the base of a modern cliff. If we should imagine 
a fault where the streams join, or consider the fragments forming 
the sides of the divided gorge to be a fault-breccia, it will not alter 
matters much: it would merely be changing one part of the 
Caithness Flags for another, or a mass of broken-up rock for the 
solid one. We cannot get over the fact that masses full of the 
fragments of a given rock are interstratified with the shales, and 
that the breccia-beds thus produced can be traced increasing in 
thickness, till they come into contact with a mass composed entirely 
of the same fragments, beyond which at last we come to the solid 
rock. Whatever was the cause of this phenomenon, it was a 
recurrent cause, as there are at least three of the breccia-beds at 
the mouth of the gorge, as seen in fig. 2 (p. 293). . 
All this is exactly what we might expect if we were here actually 
looking at the talus and deposits at the base of a cliff of Caithness. 
Flags to which the sea-stack was subsidiary. If this be so, there 
ought to be some relation between cliff and stack in the way of 
strike and dip. The question is, what relation should we expect ? 
Now, when masses of rock are separated in this way, it may he 
either along bedding-planes when these approach the vertical, as. 
inthe case of the Needles: or, more commonly, along joint-planes 
when the beds are horizontal, as in the case of the stacks of 
Duncansby. Under the latter conditions, the dip and strike of the 
mainland rocks are practically indeterminate. But these Caithness. 
Flags seem to be specially liable to overhang towards the sea, as 
shown in fig. 166 of Geikie’s ‘ Text-Book of Geology’ p. 4384 
(ed. 1882). When this is the case, any portion separating along a 
joint-plane will sooner or later heel over; its strata will have a 
high dip seaward; and the strike will be parallel to the direction 
of the joint, and so approximately of the cliff. This is exactly the 
case with the Port-Gower stack, and also with the other mass at 
Allt-a-ghruan described by Prof. Judd. All this, of course, has. 
reference to the time previous to the production of the dips in 
the Jurassic rocks, and to the formation of the breccias. 
In Jurassic times both the granite and the Caledonian Series were 
deeply buried, and the Caithness Flags did not form a mere strip, as 
now, but extended widely both westward and northward, probabiy 
forming the coast-line for a long distance to the north-north-east. 
On the south, however, they are cut off at a sharp angle, indicative 
of a fault transverse to the later post-Jurassic one. Its direction 
is possibly indicated inland by the straightness of the geological 
boundary-line drawn in its neighbourhood, and by the change of 
