part 1] AJJWIYEESART ADDEESS OF THE PRESIDE:N^T. Ixxix 



as andesites, but their felspars can often be identified as oligoclase, 

 and one type in the Knock district is a characteristic spilite. The 

 much more important eruptions, which came later, lasted without 

 apparent interruption through Llandeilo time, and continued into 

 the Bala. The sequence, as set forth by my colleague, Dr. Marr, 

 is less simple than that seen in Wales. Pyroxene-andesite lavas 

 were followed by a much more widespread outpouring of basalts, 

 and then by activity of the explosive type, which produced a 

 great thickness of breccias and ashes. Many of these show a 

 commingling of basic and acid material. To this succeeded a 

 second group of pyroxene-andesites, and finall}^ rh^^olitic lavas 

 and breccias, which are in part interstratified in the Coniston 

 Limestone G-roup. 



No distinct plutonic phase of this age is to be recognized in the 

 Lake District, but the intrusions which followed the volcanic out- 

 burst were numerous and of various petrographical types. The 

 largest masses, such as that of Ennerdale and Buttermere, are of 

 acid natm-e, sometimes with basic rocks involved in their marginal 

 pai-ts. There is no conspicuous group of dolerite sills, but many 

 of the intrusions, ranging from acid to ultrabasic in composition, 

 have assumed an irregular sill-habit. The most basic occur in the 

 Skiddaw Slates and the most acid in the Coniston Limestone 

 Grroup, suggesting a vertical distribution in accordance with density. 

 The whole suite of rocks, volcanic and intrusive, excepting the 

 early sodic types, has a calcic facies. In this connexion the 

 frequent occurrence of red garnet is worthy of remark, and, 

 whether of primary or of metamorphic origin, its chemical signifi- 

 cance is the same. The general geological relations are much less 

 clearly revealed than in Wales ; but it is probable that here too we 

 are to recognize in the Llandeilian igneous action the influence of 

 a certain element of lateral thrust directed towards the north or 

 north-north-west. It is in that direction that the large acid 

 intrusions are situated. We can verify that at a later epoch, when 

 the rocks were folded, overthrust, and cleaved by a more intense 

 thrust on the same lines, these large igneous masses, perhaps 

 larger than their exposures indicate, acted in some measure as 

 a buttress. Whether their resistance was backed by an old ridge 

 concealed beneath the Skiddaw anticline, we do not know, but the 

 existence of such an ancient barrier would explain the absence of 

 intrusions on the farther side of that line. 



It does not appear that the principal volcanic series of Wales and 



