ANN^IVERSARY ADDRESS OF THE PRESIDENT. 1 39 



sive discharges of lavas and tuffs in the centres of greatest activity 

 gradually built up piles of material, which, in the case of the Bath- 

 gate Hills in West Lothian, probably in the end exceeded 2000 feet 

 in thickness. It must be remembered, however, that the eruptions 

 took place in a subsiding area, and that even the thickest pile of 

 volcanic ejections, if the downward movement kept pace with the 

 volcanic activity, need not have grown into a lofty volcanic hill. 

 The volcanic materials are found to replace locally the ordinary 

 Carboniferous sedimentary strata. It is interesting in this regard 

 to note that during pauses in the volcanic activity, while the sub- 

 sidence doubtless was still going on, some of these strata extended 

 themselves across the volcanic tracts so as to interpose, on more 

 than one platform, a mass of ordinary sediment between the lavas 

 and tuffs already erupted and those of succeeding discharges, and 

 thus to furnish valuable geological chronometers by which to define 

 the stratigraphical horizons of the successive phases of volcanic 

 energy. 



That, in the shallower lagoons, some of the tuff-cones built them- 

 selves above the level of the water, and remained for some time 

 there before being submerged and washed down or buried under 

 sand and mud, seems to be legitimately inferred from the abundant 

 fragments of coniferous wood which are to be met with in the tuff 

 of the necks. Such wood is comparatively rare among the ordinary 

 surrounding strata, where Stigmaria and Lepidodendron are of con- 

 stant occurrence. We seem to recognize in these bits of stems and 

 trunks portions of the pines which clothed the outer slopes of the 

 volcanic cones that rose here and there above the surface of the 

 lagoons. 



Where the puys ejected streams of lava besides showers of ashes, 

 the banks or ridges which they formed not improbably rose as islets 

 out of the water. Some of these banks were at least twelve miles 

 in length, and had their materials supplied from many separate 

 vents along their surface. But that they never attained to any- 

 thing approaching the elevation which their sheets of lava and 

 tuff would have reached had they been poured out upon a stable 

 platform is admirably shown by the fact just referred to, that 

 recognizable stratigraphical horizons can sometimes be traced right 

 through the heart of these thick volcanic accumulations. One of the 

 largest areas of basalts and tuffs connected with the puys is that of 

 the Bathgate Hills, above referred to, where a depth of more than 

 2000 feet of igneous rocks has been piled up. Yet several well-known 



