Vol. 54.] A VOLCANIC SERIES IN THE MALVERN HILLS. 559 



crystals and fragments of basic rock. A remarkable feature of this 

 tuff is that the matrix is isotropic. 



Next to the eastward is a fine-grained rock, very much shattered, 

 and having its cracks filled up with calcite. In some places there 

 is a high percentage of carbonate of lime (in one instance 38*57 

 per cent., and in another 56 per cent.). The rock is, however, 

 undoubtedly a felsite, and at some points (that is, around the filter- 

 beds) is of so glassy a nature as evidently to be a devitrified 

 obsidian (48, 49, 205). The dip at this point becomes nearly 

 vertical. This type of rock is constantly repeated with more or less 

 calcite, generally less, the farther east the specimens are obtained. 



A fine-grained dyke (176) cuts across the southern end of this 

 series of rocks, striking a little south of west. It is very similar 

 in appearance to an elvan, and can be found again some way up 

 the flank of Broad Down. 



We now come to Tinker's Hill. There appears to have been 

 much less disturbance here. The rocks are sounder, there is less 

 calcite, and though there are few or no exposures on the northern 

 flank, there are some very good ones on the west, south, and east. 

 The western side was well scarped at the time of making the new 

 road past the filter-beds. It showed that the crushing and shat- 

 tering of the rocks, so marked in the Eeservoir rocks, is still a 

 conspicuous feature. On this flank was the calcareous nodule 

 mentioned by Prof. A. H. Green.^ Two slides that I have had cut 

 from this (111, 113) entirely agree with his description, ' decom- 

 posed tuff permeated by calcite.' The bed of which this is a 

 remainder extends no doubt farther north, as on the scarped bank 

 the bed is well exposed, and many fragments .of more or less 

 decomposed tuff (282) may be found on the small mound on the 

 top of Tinker's Hill along the same strike. 



Eastward of this is a bed of felsite (336). Eastward of this 

 again, on the side and on the top of the steep bank which forms 

 that flank of Tinker's Hill, is the vesicular rock which I had 

 the pleasure of pointing out to Prof. Green.^ My (sections 112 a 

 & 283) show that the rock is vesicular and amygdaloidal. I cannot 

 agree that this is a similar rock to the ' rock of Clutter's Cave,' 

 though it is with great diffidence that I venture to differ from so 

 high an authority as the late Prof. Green. My sections of the 

 Clutter's Cave rock (7 a, 155, 160, 161 & 164) show much more 

 augite, one of them (164) being quite a mosaic of that mineral, 

 whereas the Tinker's Hill rock (291 a) has much more the appeaf"- 

 ance of an andesite than a basalt. My section 283 shows an 

 extremely curious structure. It is very similar to another (180) 

 which comes from a crag much farther south, but almost exactly 

 on the same strike. In both sections are oval and circular rings 

 of some isotropic mineral : inside the rings is chalcedony. The 



^ Quart. Journ. Geol. Soc. vol. li (1895) p. 5. 

 2 Op. cit. p. 4. 



Q. J. G. S. No. 215. 2 q 



