ANNIVEESARY ADDRESS OF THE PRESIDENT. 1 59 



3. Sills. — The phenomena of sills and dykes are less clearly exhi- 

 bited among the Permian volcanic rocks than in the older series. 

 Probably the best district for the study of this subject 4s that 

 around Dalmellington. The Coal Measures are there traversed by 

 many basic sills, which have produced great destruction among the 

 coal-seams. Some of the rocks are extremely basic, including a 

 beautiful picrite like that of Inchcolm (Letham Hill, near Water- 

 side). The age of these sills must be later than the Coal Measures 

 into which they have been injected. Some of them are obviously 

 connected with the agglomerate-necks, and- the whole or the greater 

 number should thus probably be assigned to the Permian period.^ 



I have now to ask you to transfer your attention to the South- 

 west of England, where the existence of an interesting volcanic 

 group towards the base of the red sandstones and breccias of centra 1 

 Devonshire has long been known. That county and Cornwall 

 furnish one of the most striking examples to be met with in this 

 country of the persistence of volcanic action over a limited area 

 through a long succession of geological periods. There seems good 

 reason to regard the agglomerates and tuffs of the Meneage district 

 to the south of Palmouth as evidence of volcanic action in some 

 part of the Lower Silurian period.^ The vigorous and prolonged 

 eruptions of Devonian time I have already referred to. In the 

 Carboniferous rocks also, as De la Beche long ago pointed out, there 

 is evidence of renewed volcanic energy in the same region. And 

 again, after the close of the Carboniferous period, still within the 

 same restricted space, we have the remains of yet one more series 

 of eruptions. Thus during a great part of Palaeozoic time the 

 extreme south-west of England continued to be a theatre of volcanic 

 action. 



The geological age of the igneous rocks now to be referred to 

 depends upon the particular place in the geological record to which 

 we assign the remarkable breccias and sandstones with which they 

 are associated. By many geologists who have been unable to 

 recognize any true break in the red rocks from their base up to 

 the bottom of the Lias, these strata have been grouped as one 



^ See Explanation of Sheet 14, Geol. Surv. Scotland, p. 22. 



^ These rocks, which have often been described, are more particularly identi- 

 fied as volcanic intercalations, probably of Caradoc age, by Messrs. Somervail 

 and Fox, Trans. Eoy. Geol. Soc. Cornwall, 1885. See also Mr. ColHns's paper 

 in the same Transactions, vol. x. part 2, p. 52. 



