Vol. 54.] A VOLCANIC SERIES IN THE MALVERN HILLS. 561 



origin of these rings appears to be very obscure, but it seems to me 

 that they must arise from an originally vesicular structure in the 

 rock. If this be so, as they occur in an isotropic mineral on the 

 edge of an andesitic mass, it would show that this may have been 

 the original surface. 



Eastward of this is a narrow bed of felsite about 10 feet wide 

 (292). ISText, a bed of andesite (293) 54 feet wide: this, in one 

 place, has a most distinct dip of 45° to the west. My slide shows a 

 good deal of decomposed felspar and of a dichroic mineral, probably 

 an altered augite. 



Then again comes abed of felsite (295), followed by andesite 

 (296), and felsite again (297). In the last-mentioned slide is 

 a curious doubled-up thread which polarizes yellow. The beds 

 alternate until no more exposures are visible. There is a small crag 

 of brecciated dolerite close to the eastern boundary. This 

 corresponds apparently to the rock on the south-east of Hangman's 

 Hill to which I refer later on. It is not possible to measure the 

 definite width of each of these beds, but probably it is not very 

 different from that described above. 



There is one interesting rock on the south-eastern flank of 

 Tinker's Hill (289) which has all the appearance of a breccia, 

 and at times almost of a conglomerate. This also occurs on the 

 northern flank of Broad Down : it is probably a crush-breccia. 

 The great scarcity of tuffs is remarkable. 



A little farther north is an interesting crag, in which a good 

 junction between the felsites and andesites is exposed (278 & 

 279). In this case, however, the strike varies from that ordinarily 

 observed, and as seen here it is N. 30° W. There are very few 

 exposures of any sort farther north on Tinker's Hill. 



It has been my endeavour to trace these beds over the area lying 

 to the south, but the exposures are so few that the attempt has met 

 with little success up to the present. There are scattered crags 

 showing very much the same class of rocks as those in evidence at 

 Tinker's Hill. One fine crag on the south-eastern flank of Hang- 

 man's Hill shows a rock which is a porphyrite, but very near a 

 basalt (181 & 197). This is very similar to one (168) which 

 came from the floor of the Reservoir. 



A considerable quarry was opened in the north-eastern flank of 

 Broad Down by the contractor for the E-eservoir- works. Whether 

 the rock (194) is a tuff or a 'fluff (I mean by this term a fluxion- 

 breccia in which the apparent fragments differ very slightly in 

 mineral character, and in which there is not the jumble of fragments 

 usually seen in a tuff) is uncertain. The felspars are f ragmen tal, 

 and the matrix is amorphous or glassy with microlites. 



There are two other rocks to which attention may be called. 

 I was searching for the junction of the felsites and the andesites on 

 Hangman's Hill, and found a rock with a very peculiar microscopical 

 structure (180). I have had the advantage of showing it to several 

 high authorities on the subject, and it seems difficult to form a very 



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