184 IGNEOUS EOCKS AMONG THE MALVEEN CAMBEIANS. [Feb. igOt. 



Discussion. 



Mr. Peior congratulated the Author on obtaining such interesting 

 results from what at first sight appeared to be very unpromising 

 material. As regarded the ' camptonitic group ' he felt some doubts 

 concerning the nomenclature. In the case of many of the Nuneaton 

 rocks the name camptonite appeared to be justified; but the 

 Malvern rocks, in their structure and in the character of the horn- 

 blende, seemed to be more closely related to hornblende-basalts than 

 to typical camptonites. 



Prof. Watts ])oiuted out that AUport had indicated that the 

 Warwickshire ' diorites ' were a group of rocks distinct from the 

 dolerites of the Midlands. Similar rocks had since been found 

 associated with Cambrian strata in a variety of districts. In the 

 Nuneaton region the camptonites were not associated with olivine- 

 dolerites or diabases, and it was difficult to say to what this type of 

 rock in the Malvern area was related. 



Dr. J. W. Evans referred to the fact that a similar association of 

 calcite and analcime had been described by Glocker from the Moravian 

 teschenites in 1852. With regard to the use of the term camptonite, 

 he had always understood that it denoted a subdivision of the mica- 

 trap or lamprophyre-group, and, therefore, implied a predominance 

 of ferromagnesian silicates. 



The Peesideis't and Mr. Cunningham-Ceaig also spoke. 



The AuTHOE said, in reply to the President and to Mr. Prior, that he 

 did not think the amphibole-bearing rocks described greatly resembled 

 thevogesites or the typical hornblende-basalts. They appeared to be 

 more acid than the latter, and the abundant felspar of the groundmass 

 was chiefly or wholly plagioclase. Some of the amphiboles might be 

 the small representatives of the large corroded phenocrysts of the 

 hornblende-basalts, but most of them showed the needle-like form 

 so common in the lamprophyres ; though, as Mr. Prior had pointed 

 out, a resorption-border was always present. It was doubtful 

 whether more than one generation of amphibole was present or not, 

 and the rocks appeared scarcely to conform to the strict definition 

 of camptonite as given by Prof. Rosenbusch ; and it was with some 

 hesitation that the Author had regarded them as peculiar members 

 of this group, rather than as forming a new type. In reply to 

 Dr. Evans, the Author said that he had not thought it well to 

 place too much reliance on the chemical analyses given, as they had 

 been made many years ago. While recognizing the differences 

 mentioned by Prof. Watts between the olivine-bearing rocks of 

 Malvern and Nuneaton, the Author said that olivine-augite-rocks, 

 apparently devoid of hornblende, one of which approached the 

 Malvern olivine-basalts in several respects, occurred at Dosthill, 

 though still undescribed. He could give no satisfactory answ^er 

 to Mr. Cunningham-Craig's question as to the order of intrusion 

 of the difi'erent types described, since in no case known to the Author 

 were two rocks of difi'erent type seen in mutual contact. 



