86 MB. E. E. WALKER ON THE GARNET-BEARING [Feb. I904, 



pyrites are plentiful. The rock in parts is nighty vesicular — quartz, 

 calcite, and chlorite rilling the vesicles. The junction of the rock 

 with banded ash may be seen in the streams flowing into Harrop 

 Tarn, but the metamorphism is hardly appreciable. 



The quartz-porphyrites of Helvellyn and Wythburn are of the 

 same type. The silica-percentage of a quartz-porphyrite between 

 Greenburn and Wythburn is given by Mr. W. M. Hntchings as 

 60-4-5, with a specific gravity of 2*74. 



The Armboth Dyke also contains garnets. A slide (3788 : 

 PI. XIII, fig. 3) through one of these garnets shows beautiful 

 corrosion by quartz-crystals. The quartz has penetrated along 

 definite planes, and has left projecting needles of garnet. It is 

 very probable that the Armboth Dyke is closely related to the basic 

 dykes near it. By a mistake in the wording of the Geological- 

 Survey Memoir, an analysis of the St. John's quartz-felsite is 

 ascribed to the Armboth .Dyke. Mr. Harker l has shown that the 

 analysis does not belong here, and the numbers tabulated below 

 support this view : — 



Per cent. 



Si0 2 75-26 



A1 2 0, 12-85 



Fe 2 0, 017 



FeO' 1-36 



MnO 022 



CaO 0-83 



MgO 004 



K 2 501 



Na o 2(H) 



COU 0-04 



H 2 6 104 



Loss on ignition (1*20) 



99-48 

 Specific gravity = 2-048 at 16'4° C. 



VI. Garnetiferous Rocks in the Falcon-Crag Andesite-Group. 



Having dealt with the intrusive garnet-bearing rocks of the 

 district, it would be well to take the members of the Volcanic 

 Series in order. The lower part of the group consists of : — 



Banded Ashes and Breccias; 



' Streaky ' Rocks ; 



Eycott Lavas, and associated ashes and breccias; 



Falcon-Crag Lavas and Ashes. 



The Falcon-Crag Group consists of andesitic lavas and 

 ashes, typically developed round Falcon Crag on the east side 

 of Derwentwater. Ward described them in detail, and the only 

 rocks with which we need deal are those that contain garnets. 

 The lowest of these is Ward's ' No. 2 ash,' well seen at the 

 base of the small scarp beneath Falcon Crag. The ash is overlain 

 by ; No. 2 lava, 1 and is of no great thickness. Garnets are 



1 ' Chemical Notes on Lake-District Rocks ' in the ' Naturalist' for 1899, p. 150. 



