part 1] A]S^NIVERSARY ADDRESS OF THE PRESIDENT. Ixxxix 



Carboniferous, two petrographical provinces existed in Britain, 

 both of alkaline facies but with different histories. The southern 

 one was an old-established province, and preserved the spilitic 

 character which seems to be associated with prolonged gentle sub- 

 sidence. The northern province was a new one, representing a 

 reaction from the Caledonian calcic regime, to which it -was 

 genetically complementary. With this character there goes natur- 

 ally a wider diversity of petrographical types, showing progressive 

 enrichment in soda. The Irish districts of Philipstown and 

 Limerick are clearly related to Scotland, and the same is true of 

 the scant}^ development in the Isle of Man. The lavas of Derby- 

 shire and of North Somerset, as described by Mr. H. C. Sargent 

 and Prof. S. H. Reynolds respectively, present transitional cha- 

 racters. The occurrence of basalts and of certain types rich in 

 potash Avould attach these two districts to the noi-thern province ; 

 but the Derbyshu'e rocks seem also to have certain affinities with 

 the Cornish, and those of Somerset include typical spilites. 



In Northern Britain igneous activity lingered, as we have seen, 

 into the Permian. In the south it died out earlier, and here the 

 relative repose of the country was at length broken by the advance 

 of the Hercynian or Armorican crust-movements. Although these 

 Avere felt in some degree over a larger area of Britain, the extreme 

 effects — violent folding, cleavage, and overthrusting — are confined 

 to the south. Of the Caledonian zone of folding the full width 

 had been comprised within the limits of Britain, but it was only 

 the front of the Hercynian earth- wave that invaded our area. The 

 record of igneous activity related to this system is correspondingly 

 scanty. It includes first and foremost the intrusion of the gmnites 

 of Cornwall and Devon, which are found along a belt running from 

 Scilly to Dartmoor, with possible further extension in both direc- 

 tions. 



The great Caledonian intrusions of the Highlands had followed 

 the principal movements after a decided interval, though not late 

 enough to escape all effects of crushing. In the case of our 

 Hercynian granites the interval seems to have been longer. The 

 cleavage and overthrusting of the older strata were long past, and 

 the disturbance had subsided into folding of a gentler type. It is 

 well known that posthumous folding on the same roughly east-and- 

 west axes affected Mesozoic strata at a much later epoch ; and it 

 is probably by no mere coincidence that the Land's End and Carn 



