546 Prof. T. G. Bonney — North-Western Chamwood Forest. 



have been announced by Professor W. W. Watts, by whom most of it 

 was executed. As we stated at the time, we were far from being 

 satisfied with some important points in our own conclusions ; so that 

 since my return to Cambridge I have studied my specimens and 

 slices from the north-western region, which had presented to us the 

 more serious difficulties. In 1891 I had been led to regard the 

 characteristic rocks of Peldar Tor and High Sharpley as lava-flows, 

 but considered the dominant rocks of Bardon Hill to be mainly 

 pyroclastic. 1 Professor Watts, however, maintained the intrusive 

 character of the first and . second, while taking the same view as- 

 myself about the third. The lava-flow hypothesis had appeared to 

 me the more probable, because I doubted whether a mass so large as 

 the Peldar-Bardon porphyroid, if intrusive, could have maintained 

 throughout a texture so uniformly fine-grained, and I had found in 

 the Bardon quarries fragments of it embedded in rock which I then 

 supposed to be a somewhat altered tuff, closely related to the High 

 Sharpley lava. The breccias and the compact rocks of Bardon Hill, 

 the one of which seemed to pass into the other, continued to perplex 

 me, though after repeatedly studying them I became more inclined 

 to regard them as an abnormal result of some kind of flow-brecciation. 

 Having heard how greatly the Bardon Hill quarries had been 

 enlarged, and that others had been opened on Peldar Tor, Canon Hill 

 and 1 visited them last April and obtained both information and 

 specimens which were very helpful in clearing up difficulties. In 

 July I returned to this district in company with my friend Mr. P. H. 

 Pastall, F.Gr.S., in order to verify one or two matters and examine 

 a few outlying sections. 2 The specimens collected on these occasions, 

 with those already in my possession, have been carefully studied, and 

 it may be that I have benefited by the widened experience of almost 

 a quarter of a century. The result has been, as I proceed to explain, 

 to convince me that I formerly made the mistake of regarding too 

 large a number of the rocks in the north-western district as pyroclastic 

 in origin. 



The Peldar porphyroid is so uniform in its characters, megascopic 

 and microscopic, that it is practically impossible to distinguish 

 specimens got at the Tor from those of Bardon Hill. They have 

 a dull green, slightly rough ground-mass, which, under the micro- 

 scope, mainly consists of roundish or rather oblong felspars, often 

 about one-thousandth of an inch in length, separated by a filmy 

 yellowish or greenish mineral, in many cases more suggestive of 



1 In our Ckarnwood papers I accepted allresponsibility for the microscopic 

 work. 



2 I gladly tender my thanks to the owners or managers of the quarries — to 

 Mr. B. N. Everard, of Bardon Hall, for giving us the help (as he was himself 

 unable to meet us) of his foreman manager, Mr. R. B. Grant, who personally 

 conducted us over Messrs. Ellis & Everard's quarries and called our attention 

 to particular sections which other geologists had found interesting. The 

 knowledge thus acquired has led him to put aside specimens which strike him 

 as remarkable, and I am indebted to him for two of much importance, which 

 are mentioned in this paper. I have also to thank Mr. J. H. Robinson, of the 

 Peldar Tor quarry, and Mr. J. T. Briers, of the Forest Rock quarry, for much 

 kindly assistance. 



