316 



Geological Society :■ 



papers which he proposes to lay before the Society upon the volcanic 

 rocks of Britain of later date than the Chalk. In a general intro- 

 duction to the whole subject, he pointed out the area occupied by the 

 rocks, showing that they are chiefly developed along the broad tract 

 which extends from the south of Antrim, between the chain of the 

 Outer Hebrides and the mainland of Scotland, up into the Faroe 

 Islands, and even to Iceland. The nomenclature of the rocks was 

 discussed, and the following arrangement was proposed : — 





Felspathic series. 



Pyroxenic, 

 or Augitic. 





o5 



<S2 



1 

 & 



£ Hi 



la 



CD ^ 



If 



a u 



5-1 



o 



pa 



o 



+3 



o 



s 

 f-i 



o 

 Ph 



.1 



'o 



p 



* 



? 



4^ 



GO 



ci 



* 



? 



... 



CD 



c 

 EH 



* 



u 



CD 



g--g 



sJ 



s 



o 

 9 



H3 



i 



'3 s 



I. Interbedded or Contempora- 

 neous. 



A. Crystalline. 



Sheets or beds , 



B. Fragmented. 



Beds or layers 



II. Intrusive or Subsequent. 



A. Crystalline. 



a. Amorphous masses 





•Sf 



? 



? 



? 



j8. Sheets 



h. Necks 



B. Fragmentul. 

 Necks 





The age of the rocks was shown to be included in the Tertiary 

 period by the position of the volcanic masses above the Chalk, and 

 by their including beds containing Miocene plants. 



As an illustrative district, the author described the volcanic geo- 

 logy of the Island of Eigg, one of the Inner Hebrides, and brought 

 out the following points : — 



1. The volcanic rocks of this island rest unconformably upon 

 strata of Oolitic age. 



2. They consist almost wholly of a succession of nearly horizontal 

 interbedded sheets of dolerite and basalt, forming an isolated frag- 

 ment of the great volcanic plateau which stretches in broken masses 

 from Antrim through the Inner Hebrides. 



3. These interbedded sheets are traversed by veins and dykes of 

 similar materials, the dykes having the characteristic north-westerly 

 trend with which they pass across the southern half of Scotland and 

 the north of England. Yeins of pitchstone and felstone, and intru- 



