188 KYNASTON : VOLCAXIC ROCKS OF THE CHEVIOT HILLS. 
evidence, moreover, has shown that the andesites, the 
granites, and the dykes have genetic relationships to 
one another, and we may conclude therefore that in 
the Cheviot district we are dealing with three successive 
phases, belonging to the same geological period, of one 
original magma — (1) an extrusive phase, characterised 
by outpourings of andesitic lavas ; (2) a plutonic phase, 
characterised by the intrusion of the granite ; and 
(3) the fissure or dyke phase. 
It is possible that the central granite mass occupies the 
site of the main focus of the volcanic activity of this 
district, and that it has thus been intruded into the 
lower portion of the old vent or group of vents from 
which the surrounding andesitic lavas were discharged. 
The volcanic cone of Lower Old Red Sandstone times, 
which reared itself where Cheviot and Hedgehope Law 
now stand, has long since passed away. But the 
ceaseless action of denuding forces has laid bare for us 
the very heart and core, so to speak, of this ancient 
volcanic pile, with its surrounding accompaniment of 
dissected lava-flows and dykes. 
