104 MR. E. E. WALKER ON THE GARNET-BEARING [Feb. I904, 



developed, enclosing portions of the groundmass. Calcite occurs 

 in small grains and patches, often resembling felspar in outline and 

 possibly replacing that mineral. Ragged ilmenite-aggregates occur, 

 extensively altered to sphene. In the Dock-Tarn rock the chlorite 

 shows well-developed faces. Close to the junction this mineral is 

 not developed, the ash becoming white and porcellanized, and the 

 metamorphic minerals pyrites, chlorite, etc., are found at some 

 distance from the junction-line. These spotted ashes are probably 

 closely allied to the ' spilosites." 



The same miuerals occur in a very compact flinty ash enclosed 

 in garnetiferous rock, at the junction of the ' streaky ' rocks 

 and Banded Ashes at the Langstrath Gorge. The ash is whitish, 

 with greenish streaks and patches. These patches consist of chloritic 

 aggregates, with irregular masses of calcite (3765). That the 

 pressure at the junction was intense is proved by the occurrence 

 of these minerals in whorls, the minute chlorite-flakes forming 

 concentric rings. It is quite probable that the heat produced by 

 the intense pressure has been the cause of the production of new 

 minerals. 



It has been mentioned elsewhere that a considerable thickness of 

 tine flinty ash occurs in the highest parts of the district ; it would 

 seem that the flinty character has been produced by the joint 

 agency of heat and pressure. A small fault occurs in garnet- 

 bearing rocks near Black Hall in the Wrynose Valley. Fragments 

 of ash have been dragged along this line, and a flinty rock produced. 

 In other cases, the compact flinty character is due entirely to 

 contact-metamorphism. Round the intrusive Blea-Crag rocks 

 occurs on both sides of the Langstrath an aureole of flinty ash 

 and breccia, and to a great extent this compact flinty character 

 is produced by heat derived from the intrusive rock. 



EXPLANATION OF PLATES XIII & XIV. 



Plate XIII. 



Fig. 1. Slide 3751 : corroded garnet, surrounded by a plagioclase-ring, with 

 biotite in the embayinents. Magnified 12 diameters. (See p. 78.) 



2. Slide 3787 : garnet and orthoclase, surrounded by a microspherulitic 



growth of quartz and felspar. In parallel arrangement with this 

 growth elongated flakes of chlorite are seen. Magnified 16 diameters. 

 (See p. 74.) 



3. Slide 3788 : from the Armboth Dyke, showing corrosion of garnet by 



quartz. Magnified 16 diameters. (See p. 80.) 



4. Slide 3753 : ash from the Falcon-Crag Group. Magnified 16 diameters. 



(See p. 87.) 



Plate XIV. 



Fig. 1. Slide 3780 : 'streaky ' rock from Rosthwaite Fell, containing fragments 

 of granophyre. Magnified 14 diameters. (See p. 95.) 



2. Slide 3875 : 'streaky' rock from Hindside (Seathwaite), showing pale 



patches of rhyolite separated by a darker and more basic matrix. 

 Magnified 14 diameters. (See p. 1)5.) 



3. Slide 3786 : ' streaky ' rock from a loose block on the path between 



Sty-Head Tarn and Seathwaite. Magnified 8 diameters. (Seep. 97.) 



4. Slide 3839 : blue fiinty ash, above the ' streaky ' rock, Whelpside Gill 



(Helvellyu). Magnified 12 diameters. (See p. 98.) 



