82 REV. EDWIN HILL AND PKOP. T. G. BONNET ON THE 



and causing it to aggregate as a kind of network between their 

 walls. Subsequent change, perhaps devitrification, and certainly 

 the action of water, brought the rock to its present condition. 



The rock which we mentioned as occurring on the north side of 

 the Eardon-Hill Pit, and apparently identical with that of Peldar 

 Tor, has been much more fully exposed, owing to the enlargement of 

 the quarry. It is indubitably, macroscopically and microscopically, 

 identical with that of Peldar Tor. It contains rock-fragments, 

 similar to that described above. In one place a slightly more com- 

 pact variety occurs. The matrix of this does not exhibit the usual 

 spotted structure, but gives a very faint indication of a fluidal struc- 

 ture. This Peldar rock overlies, with a rather irregular base, a 

 porphyroid which bears, as will be shown in our account of the pit, 

 a general resemblance to the rock of Sharpley, and, in this, 

 fragments and possibly lenticular streaks of the characteristic Peldar 

 rock are sometimes abundant. 



We have thus been led to abandon our idea that the Peldar 

 porphyroid had a pyroclastic origin, and now regard it as a lava, 

 somewhat modified by various secondary changes. The appended 

 analyses *, kindly made in duplicate for us by Miss E. Aston, B.Sc, 

 in Professor Pam say's laboratory at University College (London), 

 indicate that, as we had been led by microscopic examination to 

 expect, the rock is rather intermediate in its position ; but on the 

 whole it is more nearly allied to the dacites than to the rhyolites. 

 Hence it should be named either an altered dacite or a porphyrite. 



3. The Porpliyroid of Blimyley. — In our last paper we called 

 attention to the very close resemblance which this rock presented to 

 a lava, but, for reasons there given, preferred to regard it as the 

 result of the alteration of a tuff which had a rather uniform 

 character. Eurtber study, however, has increased the difficulties 

 which existed in the latter view, and diminished greatly those in 

 the former. 



The fragmental character of the normal rock is due, we now 

 believe, to the pressure which has produced the schistosity, and led 

 to the development of films of sericite. To the same cause the 

 cracking of the quartzes, at anj' rate in most cases, must be attri- 

 buted. We are, however, still of opinion that a small mass of pyro- 

 clastic rock occurs near the west end of the southern ridge, and a 

 yet smaller one some distance east of it, as already described. 

 These appear to pass impercei^tibly into the normal rock, and thus to 

 support our former view ; but we can see that this difficulty in find- 

 ing a division might arise if the lava had originally a rather smooth, 

 slaggy surface, and the ash consisted of fragments and powder of an 

 identical rock. That this was really the case there is, as will 

 presently be shown, good reason to believe. The differences in 



* SiOo AI2O3 Fe.,03 FeO CaO MgO Na,0 K,0 Total. 



No. 1 71-44 10-54 3-81 2-23 533 2-95 1-93 084 99-07 



No. II 71-68 10-39 4-09 2'23 5-45 2-50 1-93 0-84 99-11 



Only one analysis was made of the amount of Na^O and Iv^O ; the loss by 

 drying and ignition was not estimated. 



