52 SCIENCE PROGRESS. 



Westmorland and other districts, and the work of Bonney 

 and Cole makes it appear that even such special structures 

 as the curious lithophysal cavities in some fresh obsidians 

 find their analogues among these ancient rocks. 



Allport had already shown (1870, 1874) that the basic 

 rocks — basalts and dolerites — of the British Isles, of late 

 Palaeozoic age, are, except for secondary changes, minera- 

 logically and structurally identical with the late Tertiary 

 rocks of similar composition in Europe. Other English 

 authors have described our older intermediate lavas with 

 the same general result, Teall's study of the Cheviot 

 hypersthene-andesites, of Old Red Sandstone age, being 

 especially noteworthy (1883). Most of these rocks are 

 considerably altered, and have been known in the field under 

 the name " porphyrite," a term largely applied to altered 

 andesites in other districts ; but one rock, the " pitchstone- 

 porphyrite " of some authors, is relatively fresh, with 

 partially glassy base, and closely resembles the Tertiary 

 andesites of Hungary and the lavas erupted from Santorin 

 during the present century. A closely allied type has since 

 been recognised in the Ordovician of Carnarvonshire. 



Some of the most interesting of recent contributions to 

 our knowledge of ancient volcanic rocks come from the 

 Carboniferous districts of Scotland and Ireland. In the 

 earlier part of the Carboniferous period the area which is 

 now Southern Scotland experienced a great outpouring of 

 volcanic material. The discharge of lavas was so copious 

 as to give rise now to broad table-lands and ranges of hills, 

 sometimes many hundreds of square miles in extent, and Sir 

 A. Geikie (2) distinguishes this phase of vulcanicity as that 

 of the " plateau " eruptions, contrasting these with the more 

 restricted and sporadic " puy " eruptions of a somewhat 

 later time in the same area. He enumerates five plateaux, 

 marking as many independent centres of volcanic activity, 

 the original extent of the largest being estimated at between 

 2000 and 3000 square miles. The materials representing 

 these great eruptions are mainly successions of lava-flows, 

 but with subordinate beds of tuff. The greater part of the 

 lavas have not yet been closely studied, and are designated 



