388 AURAN. GEOLOGY. SECONDARY STRATA. 



rocks not distinguishable from them in character, have 

 been proved to be at present so connected in Sky. 



There is still a faet in the history of the secondary 

 strata of this island, which adds some weight to the 

 opinion that the granite is posterior to them. If we trace 

 round the skirts of the Highland mountains, that line 

 of sandstone and conglomerate which reposes on them 

 and is a continuation of the strata of Arran, we shall 

 find that the conglomerate varies in character in different 

 situations, partaking invariably of the rocks on which 

 it rests. Where there is granite in the neighbourhood, 

 it contains fragments of that substance; in the neigh- 

 bourhood of Oban it contains trap, near Troup head, 

 schist, near Stonehaven, jasper: these substances being 

 severally found in the adjoining mountains. When these 

 do not exist in the mountains, their fragments are not 

 found in the conglomerate; and its composition is then 

 comparatively simple. In Arran, no fragment of the neigh- 

 bouring granite occurs in this bed ; a circumstance which 

 would be expected if the sandstone formation was of 

 a posterior date to the granite. An objection however 

 here presents itself, w r hich must not be suppressed. It was 

 demonstrated, that in one place the secondary strata are 

 in a position unconformable to that of the primary schists 

 which lie under them. These strata must therefore have 

 been deposited on the schist, which had previously been 

 deranged, either by the influence of the protruded granite 

 or by other causes. But there is no difficulty in ima- 

 gining that the protrusion of the granite had occurred 

 at different periods ; having elevated the sandstone and 

 schist together, after the former had already undergone one 

 disturbance. It is unnecessary to examine the hypothe- 

 sis which attributes these derangements to subsidence, as 

 no distinct evidence of such action has yet been produced. 



Having thus discussed all that seems necessary re- 

 specting the position of the secondary strata with regard 

 to the primary rocks, it is necessary to examine into their 



