AlfNIVEESART ADDRESS OF THE PEESIDENT. I4I 



Dasses, which project from beneath the bedded volcanic rocks of 

 Arthur Seat. Another not less remarkable instance is to be found 

 in the sills of Burntisland, underlying the basalts and tuffs of that 

 district in the immediate neighbourhood of some of the vents from 

 which these bedded rocks were erupted. 



In the third place, even where no visible vents appear now at the 

 surface near the sills, the latter generally occupy horizons within 

 the stratigraphical range indicated by the interbedded volcanic 

 rocks. It must be remembered that all the Carboniferous vents 

 were deeply buried under sedimentary deposits, and that large as is 

 the number of them which has been exposed by denudation, it is 

 probably much smaller than the number still concealed from our 

 view. The sills are to be regarded as deep-seated parts of the 

 volcanic protrusions, and they more especially appear at the surface 

 where the strata between which they were injected crop out from 

 under some of the higher members of the Carboniferous system. 

 Thus the remarkable group of sills between Kilsyth and Stirling 

 may quite possibly be connected with a group of vents lying not far 

 to the eastward, but now buried under the higher parts of the 

 Carboniferous Limestone, Millstone Grit, and Coal Measures. Again, 

 the great series of sills that gives rise to such a conspicuous range 

 of hills in the north and centre of Fife may have depended for its 

 origin upon the efforts of a line of vents running east and west 

 through the county. Some vents indeed have been laid bare in 

 that district, especially in the conspicuous group of the Saline Hills, 

 but many more may be concealed under higher Carboniferous strata 

 farther east. 



In the fourth place, the materials of which the sills consist link 

 them in petrographical character with those that proceeded from 

 the puys. The rocks of the intrusive sheets around Edinburgh and 

 Burntisland, for instance, are very much what an examination of 

 the bedded lavas in their neighbourhood would lead us to expect. 

 There is, of course, the marked textural difference between masses 

 of molten rock which have cooled very slowly within the crust of 

 the earth and those which have solidified with rapidity at the surface. 

 There is likewise the further contrast between the composition of the 

 volcanic magma at widely separated periods of its extravasation. 

 At the time when the streams of basalt flowed out from the puys, 

 its constitution was comparatively basic, in some localities even 

 extremely basic. Any sills dating from that time may be expected 

 to show an equal proportion of bases. But those which were injected 



