1 62 PROCEEDINGS OP THE GEOLOGICAL SOCIETY, 



porphyries " occurring among them/ a statement which, if petro- 

 graphically accurate, would suggest the uprise of a later more acid 

 lava in some of the vents. 



Though much remains to be done in this region before an ade- 

 quate account can be given of the interesting series of eruptions 

 which concludes the long volcanic history of the South-west of 

 England, enough is known to indicate the general character of the 

 phenomena. The eruptions were on even a feebler scale than 

 those of the Permian period in Scotland, but they seem to have 

 resembled them in their general character. Small puy-like vents 

 were opened, from which dark scoriaceous lavas and showers of 

 gravelly tuff and stones were discharged over the floor of the inland 

 sea or lake-basin in which the red sandstones and breccias were 

 accumulated. These outflows and explosions took place too, as in 

 Scotland, towards the beginning of the deposition of the red strata, 

 and entirely ceased long before that deposition came to an end. 

 In each area the eruptions mark the close of Palaeozoic volcanic 

 activity in Britain. The varied and recurrent volcanic episodes 

 which marked the passing of each successive geological period from 

 the Archaean onwards now definitely terminate, not to be resumed 

 until after the passing of the whole of the vast cycle of Mesozoic 



X. TERTIARY. 



The entire absence of any evidence of volcanic eruptions over the 

 area of the British Isles during so considerable a part of geological 

 history as the whole of Mesozoic time is a most striking f act.^ "When 

 we reflect that the stratigraphical records of this prodigious lapse of 

 geological time are singularly complete in this country, that they 

 are not only spread out over the half of England, but are found 

 also across a considerable tract of the north of Scotland, as well as 

 on a more limited scale in the north of Ireland, we feel that this 

 want of any trace of contemporaneous volcanic activity almost 

 certainly arises from the absence of eruptions over the regions where 

 these records were accumulated. The gradually dwindling subter- 

 ranean energy of Palaeozoic time was followed by a vast period of 

 quiescence, which, so far as we yet know, remained entirely un- 

 broken until after the beginning of the Tertiary period. 



Having only a few years ago published a detailed account of what 

 seem to me to have been the more important characteristics of the 



^ Ibid. p. 204. ^ The same fact is observable throughout most of Europe. 



