280 



Reports and Proceedings. 





Felspathic series. 



Pyroxenic, 

 or Augitic. 





d 

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II 



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.a o. 

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§ 

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t 



p. 

 o 



PL, 



2 

 •g 



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« 

 * 



p 



* 



* 



"3 

 pq 



* 



* 



P 



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 boo 



P 



o 



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p 



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£ bo 



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* 



I. Intekbedded or Contempora- 

 neous. 



A. Crystalline. 



Sheets or beds 







P 



P 

 'f' 



* 

 * 



* 

 ... 



* 



B. Fragmental. 



Beds or layers 







II. Intrtjsiye or Subsequent. 



A. Crystalline. 



a. Amorphous masses 



* 



* 



;8 Sheets 



y. Dykes and veins ^... 



* 



* 



p 



S. Necks .. 





B. Fragmental. 

 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. Veins of pitchstone and felstone, and intru- 

 sive masses of quartziferous porphyry, like some of those which in 

 Skye traverse or overlie the Lias, likewise intersect the bedded dole- 

 rites and basalts of Eigg. 



4. At least two widely separated epochs of volcanic activity are 

 represented by the volcanic rocks of Eigg. The older is marked by 

 the bedded dolerites and by the basalt veins and dykes which, though 

 strictly speaking younger than the bedded sheets which they inter- 

 sect, yet probably belong to the same continuous period of volcanic 

 action. The later manifestations of this action are shown by the 

 pitchstone of the Scuir. Before that rock was erupted, the older do- 



