928 DR ROBERT CAMPBELL ON 
Margie series on the one side of the Central Valley and the rocks of Ordovician age on 
the other. The crushed spilitic lavas with their accompanying cherts and jaspers find 
their counterpart in the Arenig voleanic series of the Southern Uplands ; the sediments 
of the Margie series, resting unconformably on the former group, and derived in part at 
least from it, may fairly be compared with certain higher horizons in the Ordovician of the 
South of Scotland. The paleeontological evidence obtained at Stonehaven, on the other 
hand, favours the view that the Jasper and Green-rock series is Upper Cambrian. It is 
possible, however, as Dr Peacu* has pointed out, that the Highland Border rocks will 
ultimately be found to include representatives of both the Arenig and Upper Cambrian 
formations. But from our present point of view the distinction between Upper Cambrian 
and Ordovician as the position of the series as a whole is of minor importance. The 
vital question is: In the light of recent discoveries can they possibly be regarded as 
pre-Cambrian? Our lack of knowledge of the life of pre-Cambrian times may, it is 
true, forbid dogmatic assertion on this point; but it will be admitted, I think, by most 
geologists that the range of genera obtained at Stonehaven and Aberfoyle, taken 
together with the lithological resemblances cited above, affords very strong, if not con- 
clusive, evidence against these rocks being pre-Cambrian. 
II]. Tae SrructuraL RELATIONS oF THE [?] Upper CaMBRIAN. 
Along their northern boundary the Cambrian rocks are separated from the Dalradian 
Schists by an overthrust fault, which, during low tides, may readily be traced from the 
southern shore of Craigeven Bay to Garron Point. Its position is indicated by the 
occurrence of a dolomitic fault rock, creamy white on a fresh fracture, but weathering 
to a rusty brown colour. In Craigeven Bay the dolomite attains a maximum thickness 
of about 40 feet. Microscopic sections show that it is undoubtedly a fault rock, made 
up largely of carbonates, but containing here and there recognisable angular fragments 
of the spilitic lavas. Thin veins of similar rock are developed along some of the minor 
movement planes in the green rocks themselves. The overthrust character of the 
fault is well seen from the position of the dolomite bed on the cliff on the north side 
of Craigeven Bay, and again from the fault feature south of the Skatie Shore.. The 
fault is not indicated in the first edition of the one-inch map of the Geological Survey, 
but has been inserted by Mr Barrow in the revised edition. It may be regarded as a 
continuation of the Highland Boundary fault. 
The southern boundary of the Jasper and Green-rock series at Ruthery Head has 
hitherto been mapped as a fault separating the schistose rocks from the Old Red 
Sandstone. During the present research, however, evidence has been obtained which 
proves that the junction is really an unconformable one, and that the overlying beds 
are of Downtonian age. 
* Presidential Address to Section C, British Association, Dundee, 1912. 
