196 
PROFESSOR T. J. JEHU AND DR ROBERT CAMPBELL ON 
and there can be no doubt that they were originally of the nature of dunites. 
Du Toit * has noted the occurrence of diallage and enstatite. The fine-grained 
compact serpentines at Maol Ruadh often show no trace either of the original 
minerals or textures. Sometimes, however, they contain corroded crystals of albite. 
The interpretation of these rocks presents considerable difficulty, but we have arrived 
at the conclusion that they represent serpentinised albite gabbros. 
The albite gabbros at Maol Ruadh consist essentially of a coarsely crystalline 
granitic aggregate of albite and compact green hornblende. The albite is of the 
same type as that of the albite diabases, and represents doubtless albitised lime-rich 
plagioclase. In one instance we found the felspar of the gabbro to be saussuritised. 
Locally both the felspars and the hornblende are replaced in whole or in part by a 
green serpentinous substance similar in its optical properties to the material of the 
compact serpentines. Whether the final product is compact serpentine, a serpentine 
with corroded albites, or an albite gabbro depends on how far the process of 
serpentinisation has progressed. The available evidence shows that albitisation has 
preceded the serpentinisation. It is of importance to note, however, that veinlets of 
water-clear albite, similar to those found in the hornblende schists (see p. 198), 
traverse not only the fractured fresh hornblende of the albite gabbro, but also the 
partially serpentinised constituents. Hence there was also an introduction of albite 
at a later phase in the history of the rock. 
The serpentines usually contain in greater or less abundance secondary carbonates 
after olivine. When this process of replacement is complete the resulting rock (see 
Plate IV, fig. 5) is a ferruginous dolomite, in which the original mesh structure of the 
dunite serpentine may still be seen, but in which the only original minerals remain- 
ing are the chrome spinels. This development of a ferruginous dolomite at the 
expense of the serpentine was recognised by Du ToiT.f Dolomites, commonly 
creamy-white in colour, but sometimes tinted with delicate shades of green and 
rose-red, and weathering with a reddish-brown crust, now form perhaps the major 
portion of the complex, and there can be no doubt that they are in large measure 
“ pseudomorphs ” after serpentine. Some of the dolomite of course, notably the 
veins which intersect the adjacent conglomerates of the Lower Old Red Sandstone, 
is vein-rock of the ordinary type. The dolomite is sometimes veined with jasper 
and chalcedony, deposited at a later period from solutions charged with silica. 
Like the rocks of the similar complex at Toward and Inellan,| the serpentines 
sometimes, for example near the ruins of Bofrishlie Farm, show evidence of intense 
shearing, and have apparently shared in the movements which induced the foliation 
of the rocks to the north. 
G-abbros and serpentines occur in association with spilitic lavas in Ayrshire, in 
Cornwall, and elsewhere. In discussing the spilitic sequence Flett and Dewey § 
* Trans. Edin. Geol. Soc., vol. viii, p. 323, 1905. f Ibid. 
J Mem . Geol. Survey : Geology of Oowal, p. 73, 1897. § Loc. cit., p. 243. 
