J. W. Judd — Secondary Rocks of Scotland. 71 



highly probable that the first period of igneous activity (namely, 

 that of the eruption of felspathic lavas from the great volcanos) 

 was contemporaneous with the Eocene sedimentary formations ; the 

 second period, that of the great and prolonged outbursts of basaltic 

 lavas from the same vents, was certainly that of the Miocene ; while 

 the third period, or that of the formation of the '-'iDuys," may, with a 

 great show of probability, be correlated with the Pliocene. 



The igneous activity during the Tertiary period in the Northern 

 Hebrides appears to have extended in all its magnitude, and to have 

 exhibited similar stages in its development, far to the southwards, 

 as is illustrated by the rocks of Arran, Antrim, and the Mourne 

 Mountains. But even this tract, extending 400 miles from north to 

 south, which was characterized by grand volcanic phenomena during 

 the whole of the Tertiary period, can only be regarded as a portion 

 of the great belt of volcanos which at that epoch extended through 

 Greenland, Iceland, the Faroe Islands, the Hebrides, Ireland, Central 

 France, the Iberian peninsula, the Azores, Madeira, Canaries, Cape 

 de Verde Islands, Ascension, St. Helena, and Tristan d'Acunha, and 

 which constituted, as shown by the recent soundings of H.M.S. 

 ' Challenger,' a mountain-range comparable in its extent, elevation, 

 and volcanic character with the Andes of South America. The 

 admirable manner in which the relations between the Volcanic and 

 Plutonic rocks are exhibited in the old volcanos of the Hebrides, 

 renders them of special interest to the geologist ; and the further 

 illustrations of the same phenomena which are afforded to us by the 

 relics of a still older series of volcanos, are made more clear and 

 striking by the aid of their analogies. 



The Neioer Palceozoic Volcanos. — In the district of Lorn we find 

 a great series of old felspathic lavas which, in their lower part, 

 alternate with conglornerates and sandstones, and which, in their 

 higher portions at least, appear to be of subaerial origin. It is 

 evident that we have here the relics of what was once a widely 

 spreading plateau, made up of lava-streams, like that of Tertiary age 

 already described. These rocks were evidently formed long subse- 

 quently to the Lower Silurian strata, but before any of the Secondary 

 sediments were deposited. 



The central and southern districts of Scotland exhibit enormous 

 masses of igneous rocks, in part at least of subaqueous origin. These 

 exhibit a very close similarity in petrological character with the lavas 

 of Lorn, and are shown, by the interbedded and contemporaneous 

 fossiliferous sediments associated with them, to range in age from 

 the Lower Old Eed Sandstone to the Lower Carboniferous. 



Along the whole line of the Grampian Mountains we find a number 

 of granitic masses connected with a wonderfully complicated series 

 of veins and dykes of rocks of similar composition. These igneous 

 intrusions, which disturb and metamorphose the surrounding strata, 

 are evidently, as shown by Murchison and Geikie, of far later date 

 than the Lower Silurian, but are earlier than the Secondary strata. 



Concluding, as we cannot avoid doing, that these igneous intru- 

 sions and the subaerial and subaqueous lavas of similar composition 



