204 PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
and probably at considerable depth, has resulted in the formation of schists both 
from hypabyssal and effusive igneous rocks and from cherty sediments associated 
with the Lower Series. The hornblende schists, which are the dominant rock type 
of the belt, represent, as has been already shown, original hypabyssal diabases and 
perhaps even gabbros ; the calc-chlorite schists are altered spilitic lavas ; the quartz 
schists are metamorphosed cherty sediments.. The sediments underwent contact 
metamorphism prior to the development of foliation. 
The extreme mineralog-ical and structural changes of those rocks, as compared 
with the corresponding rocks to the north-west, may be accounted for by the follow- 
ing factors : {a) intense local shearing ; (b) probably an original greater cover, since 
the included metamorphosed lavas and iron cherts belong to a lower horizon than 
that of the unaltered lavas and cherts to the north ; (c) the fact that the dynamic 
metamorphism may have followed close on the intrusion of the hypabyssal types, 
while these rocks and the adjoining sediments were still in a somewhat heated 
condition. 
The period at which the shearing took place is an open question. Should the 
diabases and gabbros prove to have been intruded in pre-Margie times — as seems 
most likely,— then the shearing, which followed close on the intrusion, must belong 
to a phase of the pre-Margie movements of elevation and compression ; on the other 
hand, it is possible that it may be a phase of the post-Margie Folding movements. 
Fragments of the rocks of the belt have not so far been recognised either in the 
Margie Grits or in the Leny Grits. 
The belt is bounded on both sides by faults— on the south by the Jasper Fault, 
an overthrust which brings it in contact with the Lower Old Red Sandstone ; on the 
north by a normal fault which brings it in juxtaposition sometimes with the Margie 
Grits, sometimes with different members of the Black Shale and Chert Series. 
The Relation of the Highland Border Rocks to the Leny Grits.— The Leny Fault 
marks a line or lines of dislocation between the Highland Border Rocks and the 
Leny Grits. It hades at high angles to the north-west, and at places is almost 
vertical. As shown on the map and sections, figs. 3-10, the Leny Grits abut in 
some places against the Upper or Margie Series, and at others against the Lower 
or Black Shale and Chert Series. Cherts and Black Shales are nowhere seen in 
situ to the north-west of the Leny Fault. 
The characters of the Margie Grits and Leny Grits have already been compared 
(pp. 200, 201) and their resemblances and differences discussed. It is important to 
note that clastic micas are common in the sediments of both series. The view held 
by Mr Barrow, that the Margie Series can be distinguished from the Highland Rocks 
to the north by the presence of clastic micas in the former and their absence in the 
latter, cannot be maintained, at any rate so far as the Aberfoyle district is concerned. 
If that is to be the criterion for separating the Highland Border Rocks from 
the more metamorphosed rocks of the Highlands in which the micas have been 
