ANNIVERSARY ADDRESS OF THE PRESIDENT. QI 



On both sides of the country, along the shores of Ayrshire on the 

 west and those of Kincardineshire and Porfarshire on the east, 

 the volcanic group has been admirably dissected by the waves. The 

 lava-beds have been cut in vertical section, so that their structure 

 and their mode of superposition, one over another, can be con- 

 veniently studied, while, at the same time, the upper surfaces of 

 many of the flows have been once more laid bare as they existed 

 before they were buried under the accumulations of the lake in 

 which they were erupted. 



Though distinctly bedded, the porphyrites show none of the 

 regularity and persistence so characteristic of the more basic lavas 

 of Carboniferous and of Tertiary time. Some of them are not more 

 than from 4 to 10 feet thick, and generally on the coast-cliffs they 

 appear to be less than 50 feet. A continuous group of sheets can 

 sometimes be traced for 10 miles or more from the probable vent of 

 discharge. 



That these lavas were erupted in a markedly pasty condition may 

 be inferred from certain of their more prominent characteristics. 

 Sometimes, indeed, they appear as tolerably dense homogeneous 

 masses, breaking with a kind of prismatic jointing; but more 

 frequently they are strongly amygdaloidal, and sometimes so much 

 so that, as already stated, the amygdales form the larger proportion 

 of their bulk. Where the secondary infiltration-products have 

 weathered out, the rough scoriform rock looks as if it might only 

 recently have been erupted. In a few instances I have observed an 

 undulating rope-like surface, which reminded me of well-known 

 Yesuvian lavas. Usually the top and bottom of each sheet assume 

 a strikingly slaggy aspect, which here and there is exaggerated to 

 such an extent that between the more solid and homogeneous parts 

 of two consecutive flows an intermediate band occurs, 10 or 12 feet 

 thick, made u^ of clinker-like lumps of slag, the interspaces being 

 fiUed in with hardened sand. In some cases these agglomeratic 

 layers may actually consist in part of ejected blocks ; but the way 

 in which many of the lavas have cooled in rugged scoriaceous 

 surfaces is as conspicuous as on any modern coulee. The loosened 

 slags, or the broken-up cakes and blocks of lava, have sometimes 

 been caught up in the still moving, pasty current, which has con- 

 gealed with its vesicles drawn out round the enclosed fragments, 

 giving rise to a mass that might be taken for a breccia or agglo- 

 merate. Now and then we may observe that the upper slago-j 

 portion of a sheet has assumed a bright red colour from the oxida- 



