2Q2 



MR. K. H. RASTALL ON THE 



[May 1906, 



been briefly described by the late E. E. Walker. 1 This consists of 

 a somewhat lenticular mass of basic rock, about a quarter of a mile 

 long, which at its eastern extremity runs out in a beautiful fringe 

 of dyke-like prolongations, intruded along the bedding-planes of 

 the Skiddaw Slates. Associated with this are some good examples 

 of acid dykes, which are evidently of later age, and show some 

 striking variations. (See sketch-map, fig. 2, below.) 



Fig. 2. — Sketch-map of the igneous complex of Burtness Combe, 

 Buttermere. 



•^ X . X X ,*v^.,\,V* 



BURTNE-S 

 '■Scale:- 3 inches — 2 ^«^/c':VO.::A'^Vv//^^v\^":';V-'>'-'v.V 



Skiddaw Slates 



Borrowdale 

 Volcanic Series 



xx'x I Granophyre 



Acid Dykes 



8 B ~l Basic Intrusions 



The basic rock may be regarded as a small laccolite, which, 

 owing to the present high south-easterly dip of this part of the 

 district, is exhibited practically in cross-section. The basic intrusion 

 is by no means uniform throughout, but shows some interesting 

 variations. At the margin it is a fine-grained dark-green rock, 

 and the same type is also found in the fringes at the eastern end. 

 Passing towards the centre of the main mass, the rock is seen to 

 become gradually coarser in texture and lighter in colour, until at 

 the centre it is a moderately-coarse rock of doleritic character, with 

 a distinctly pink colour in irregular patches. According to Walker 2 

 the silica-percentage of the basic margin is (from two analyses) 

 50-12 and 49'52. In a specimen of the coarse pink-spotted rock 

 from the centre, I found 56-03, 56-10, and 56-16 per cent, of 

 silica; there is, then, evidently a considerably higher silica-percentage 

 in the middle. 



Quart. Joura. Geol. Soc. vol. lx (1904) p. 83. 



Ibid. p. 84. 



