ANNIVEESAKY ADDRESS OF THE PEESIDENT. 127 



many examples may be found where piiys have risen in the inter- 

 space between the limits of the eruptions of two plateau-areas. 

 Thus the tract between the Campsie plateau-eruptions on the west 

 and those of the Garlton Hills on the east was dotted over with 

 puys. 



While the central valley of Scotland continued to be the chief 

 theatre of volcanic activity during the later section of the Carboni- 

 ferous period with which we are now dealing, scattered groups of 

 puys appeared far beyond that region. Though the phase of energy 

 now exhibited, if we judge of it from the amount of material dis- 

 charged and the extent of the areas over which that material was 

 distributed from any single centre, was of an increasingly feeble 

 character, it manifested itself throughout a much more extensive 

 region than that within which the plateau-eruptions had been con- 

 fined. Passing beyond the broad plain of the middle of Scotland we 

 find a chain of puys extending down Liddesdale on the southern 

 flank of the Silurian uplands. Traces of a more distant group 

 occur in the south of the Isle of Man.^ As we follow the suc- 

 cessive subdivisions of the Carboniferous system along the Pennine 

 chain from the Border into the heart of England, though the 

 natural sections are abundant, we meet with no trace of included 

 volcanic rocks until we reach Derbyshire. The whole of that wide 

 interval of 150 miles, so far as the present evidence goes, remained 

 during Carboniferous time entirely free from any volcanic eruption. 

 Over the sea- floor of the Carboniferous Limestone, in what is now 

 the heart of England, vents were opened from which the sheets of 

 ' toadstone ' were ejected, which have so long been a familiar 

 feature in English geology. Beyond this limited district the Car- 

 boniferous formations of the south-west of England remain, on the 

 whole, devoid of contemporaneous volcanic intercalations. In the 

 south-western counties traces of Carboniferous volcanic action have 

 not yet been recognized except in Devonshire, where they were long 

 ago noticed by Sir Henry de la Beche in the early days of the Geo- 

 logical Survey.^ To the west of Dartmoor, Brent Tor and some of 

 the surrounding igneous masses may mark the positions of eruptive 

 vents during an early part of the Carboniferous period.-^ 



1 J. Home, Trans. Geol. Soc. Edin. vol. ii. (1874) p. 332 et seqci. 



^ * Report on the Geology of Cornwall, Devon, and West Somerset' (1839), 

 p. 119 et seq. 



3 ' The Eruptive Rocks of Brent Tor ' (Mem. Geol. Survey), by F. Rutley. 

 1878. 



