Vol. 60. "J ROCKS OP THE BORROWUALE VOLCANIC SERIES. 83 



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Immediately south of Stony Tarn a darker grey rock forms a 

 mosaic with, and seems to be intrusive into, the purple-banded ash. 

 Sections of this rock (3841-3846) show a granular aggregate 

 of quartz and felspar. Irregular patches of the green tibrous 

 mineral, together with aggregates of strongly-pleochroic biotite- 

 rlakes, occur. Garnets are abundant : they show the same 

 characters as the garnets found in the altered ash, being irregular 

 in outline and of a very spongy nature, freely penetrated by quartz- 

 grains. We have, then, in this rock, three minerals found in the 

 metamorphosed ash ; if this rock be intrusive, and there seems no 

 reason to doubt it, a considerable amount of absorption of the meta- 

 morphosed ash must have taken place. 



It has been noticed above that aggregates of uralite- and mica- 

 tlakes occur in the dyke-rocks of Criscliffe Kuotts. That these 

 minerals also occur as products of metamorphism is rather suggestive. 

 Absorption certainly does take place, but it would perhaps be going 

 too far to ascribe the formation of these intermediate rocks of the 

 dykes to such a process of absorption by an acid rock. The presence 

 of the same minerals in the altered rocks and in the dykes renders 

 if a somewhat difficult task to distinguish between a purple dyke- 

 rock and an altered Eycott Lava. Above the granite of Oliver Gill 

 both dyke and altered rock may be seen, and it is almost impossible 

 in the held to say where the dividing-line comes. Another example is 

 seen north of Great How, on the extreme edge of the rock-exposure. 

 Here a black rock occurs, apparently intrusive. Under the micro- 

 scope large phenocrysts of plagioclase are observed, often very much 

 broken and corroded, and penetrated by aggregates of biotite-flakes. 

 Large mica-flakes also occur. ^Microscopically, the rock resembles 

 a highly-altered Eycott Lava. 



The Eskdale Granite itself rarely contains garnets. In a section 

 of this rock a small fragment of garnet occurs associated with quartz 

 and biotite. The quartz nearly envelops the garnet, and a large 

 biotite-flake has been produced as the result of the action of the 

 quartz on the garnet. Chlorite occurs as an alteration-product of 

 the garnet (3927). 



IV. The Intrusive Complex of Burtness Combe, Buttermere. 



Seeing that the Buttermere Granophyre comes into contact with 

 the Eskdale Granite at the foot of Wastwater, the basic dykes on 

 Yewbarrow might be supposed to come from the Buttermere rock. 

 Accordingly I visited a basic intrusion mapped by Ward on the 

 western ilank of Bur tn ess Combe, Buttermere. It forms a roughly- 

 oval mass, and a contorted felsite-dyke is mapped as occurring below 

 it. This may be so, but certainly a contorted felsite-dyke runs from 

 the south-eastern corner of the intrusion right through it, and is 

 continued on to the main granophyre-intrusion. This varies from a 

 light-brown to a greyish, or more rarely pink, rock, and shows good 

 banded structure. 



The basic rock through which it passes was described by Ward 

 as a quartzose diorite. It is, however, a good diabase containing 



