Vol. 60.] BOCKS OP THE BOEEOWDALE VOLCANIC SEEIES. 97 



flinty 'streaky' rock. In section (37S6 : PI. XIV, fig. 3) it shows 

 oblong orthoclase-crystals always oriented in the direction of the 

 ' streaky ' lines. There are bands of light and dark matrix, the 

 former containing fibres of a brownish mineral which gives straight 

 extinction parallel to the length of the fibres. Aggregates of quartz- 

 grains in oval patches, possibly representing original vesicles, contain 

 the same fibrous mineral. The rock is frequently faulted. 



The second example of a { streaky * lava is furnished by the rock 

 obtained from the garnet-breccia of Ore Gap. Slightly turbid pink- 

 white felspar, giving the extinction-angle of oligoclase, occurs in 

 rounded and corroded crystals, thinning out in the direction of flow. 

 Fine-grained andesitic fragments have been caught up and rounded. 

 The groundmass is that of a true rhyolite, exhibiting the 

 characteristic appearance of light and dark patches. Along certain 

 lines the structure becomes coarse and lenticular, and linear aggre- 

 gates are seen, consisting of idiomorphic felspars in quartz. Cubes 

 of pyrites of a reddish tinge are common, especially in the more basic 

 streaks ; they usually possess a dark interior, and are surrounded 

 by a ring of epidote. Ilmenite and apatite occur. 



There are undoubted lavas in the Haweswater District. One of 

 these, a typical rhyolite with a silica-percentage of 82*25, is 

 mentioned by Mr. Harker 1 as occurring a quarter of a mile 

 south-east of Walla Crag. A garnetiferous andesite occurs 

 at the top of the series at "Woof Crag, on the Xaddle side of Hawes- 

 water. This yielded a silica-percentage of 59*70, and Mr. Harker 

 tabulates its specific gravity as 2 , <>08. 



Above the ■ streaky " rocks comes a great thickness of banded 

 ash and breccia, filling up the syncline in the highest part of 

 the district. A zone of crush-breccia ti on has been mentioned 

 as occurring at the junction over wide areas. This plane of crushing 

 does not, however, keep to the same horizon. It can be traced 

 from the eastern shore of Sty-Head Tarn, over the watershed and 

 down to Lingmell Beck. On the slopes of Lingmell * streaky ' rock is 

 developed both above and below the line of crush-brecciation. The 

 phenomena rather suggest a reduplication of • streaky ' rocks by 

 thrusting. 



' Streaky ' rocks are developed on Illgill Head ; between them and 

 the Lingmell rocks occurs a band of andesite and Eycott Lavas. 

 The Illgill-Head rocks have not been carefully mapped ; but this 

 intercalation of Eycott Lavas between two bands of * streaky ' 

 rock is particularly suggestive, when the succession in the Hawes- 

 water area is considered. These patches of • streaky ' rock developed 

 on Illgill Head and at Stirrup Crag (Yewbarrow), may, however, 

 occur only in faulted areas, for the ' streaky ' rocks elsewhere form 

 a complete series. 



The rocks immediately above the 'streaky' rocks consist of a 

 greenish ash and breccia containing fragments of ' streaky ' 



1 ' Chemical Xotes on Lake-District Rocks' in the 'Naturalist' for 1899. p. 57 



Q. J.G.S. No. 237. h 



