394 Proceedings of the Royal Physical Society. 



sandy beds, the Keuper subdivision. This surmise has re- 

 ceived unexpected corroboration through evidence afforded 

 by fossils. A large volcanic neck or vent was found about 

 the centre of the island, between Brodick and Black- 

 waterfoot, which pierces the surrounding formations from 

 the Lower Old Red Sandstone up to the red Triassic marls. 

 A large detached mass of strata, acres in extent, composed 

 of red and whitish marls and black shales and limestone 

 bands, occurs embedded in the agglomerate and intrusive 

 igneous rocks that fill the vent. From the dark shales of this 

 mass Mr Macconochie obtained a suite of characteristic fossils 

 of the Avicula contorta zone, showing that the black shales 

 are of Rhaetic age.^ The underlying red marls are identical 

 with those which form the highest beds of the supposed Trias 

 in the immediate vicinity. But this does not exhaust all 

 the evidence obtained from fossils afforded by this vent, for 

 other masses of sedimentary strata were found embedded 

 among the volcanic materials. One of these masses afforded 

 a large suite of fossils, determined by Mr E. T. N^ewton to be 

 of Lower Lias Age, and some limestone blocks have been 

 proved by him to contain characteristic Upper Cretaceous 

 forms.2 Thus the vent is shown to be of later date than the 

 Upper Cretaceous, and is doubtless coeval with the great 

 volcanic period of Antrim, Mull, and Skye. Further, as 

 most of the types of the plutonic and intrusive igneous 

 rocks of the island are found to have welled up this vent, 

 a strong presumption is raised that the great plutonic 

 masses and intrusive sheets found outside the neck are also 

 of Tertiary age ; but what appeals most to the imagination 

 is the impressive evidence thus obtained, that Secondary 

 Strata must have overlain this part of the south of Scotland 

 which have been entirely removed by denudation since 

 Tertiary time. 



The work done in Scotland during the period under 

 review has thoroughly established the paramount value of 

 Palaeontology in the interpretation of the geological structure 

 of the country. 



1 M&m, Geol. Sur.j "Summary of Progress for 1899," pp. 132-134, 1900. 



2 Mem, Geol. Sur., "Summary of Progress for 1899," pp. 132-134, 1900. 



