ANNIVEESARY ADDRESS OF THE PRESIDENT. 1 25 



volcanic activity in Central Scotland during Carboniferous time. 

 The plateau- type of eruption ceased and was not repeated, but a new 

 type arose, to which I would now call your attention. 



(B) The Puts. 



After the beginning of the Carboniferous Limestone period in the 

 British area, when eruptions of the plateau-type had ceased, volcanic 

 activity showed itself in a different guise both as regards the nature 

 of its products and the manner and scale of their discharge. Instead 

 of the widely extended lava-sheets and tuffs piled above each other 

 to a thickness of many hundred feet and over areas of hundreds of 

 square miles, we have now to study the records of a feebler phase 

 of vulcanism, where scattered groups and rows of Puys, that is, of 

 small volcanic cones, threw out in most instances merely tuffs and 

 these often only in trifling quantity, though here and there their vents 

 poured forth also lavas and gradually piled up more important vol- 

 canic ridges. The evidence for these less vigorous manifestations of 

 volcanic activity is furnished (1) by layers of tuff and sheets of 

 basalt intercalated among the strata that were being deposited at the 

 time of the eruptions, (2) by necks of tuff, agglomerate, or different 

 lava-form rocks that mark the positions of the orifices of discharge, 

 and (3) by sills and dykes that indicate the subterranean efforts of the 

 volcanoes. The comparatively small thickness of the accumulations 

 usually formed by these vents, their extremely local character, the 

 numerous distinct horizons on which they appear, and the intimate 

 way in which they mingle and alternate with the ordinary Carboni- 

 ferous strata are features which at once arrest the attention of the 

 geologist, presenting, as they do, so striking a contrast to those of 

 the Plateaux. 



Prom the clear intercalation of these volcanic materials in suc- 

 cessive platforms of the Carboniferous system, the limits of geological 

 time within which they were erupted can be fixed with considerable 

 precision. It may be said that, in a broad sense, they coincided 

 with the deposition of the Carboniferous Limestone, and certainly 

 it was during the time of that formation that the eruptions which 

 produced them reached their greatest vigour and widest extent. 

 Here and there, however, indications may be found that the phase 

 of the Puys began during the time of the Calciferous Sandstones, and 

 that it may perhaps have been contemporaneous with the later 

 eruptions of the Plateaux. At Edinburgh, for example, the older 

 lavas and tuffs of Arthur Seat, Calton Hill, and Craiglockhart 



