vol. 60.] igneous rocks of poxtesford hill. 485 



Discussion. 



The President said that he felt that the detailed petrographical 

 descriptions given by the Author were of much value. He stated 

 that hopes had been held out that Prof. Lapworth would come to 

 the Meeting, and he felt sure that all the Fellows present would 

 regret his absence and the cause of it. In these circumstances, he 

 asked the Secretary to read some remarks which Prof. Lapworth 

 had kindly contributed to the discussion. 



Prof. Watts said that Prof. Lapworth had hoped to attend the 

 Meeting, and to speak upon the stratigraphical aspect of the question, 

 but unfortunately he was not well enough to be present. He had, 

 however, asked him to say that 



' the tuffs and lavas of Poutesford were clearly faulted against Cambrian strata 

 on the western side of the hill, while Eala Beds were exposed at several points 

 in the valley running practically all along its eastern side. These Poutesford 

 rocks, however, were merely a portion of a broken band of Uriconian rocks 

 occurring at intervals from Plealey on the north to Linley on the south, and 

 following at once in contact with Upper Longmyndian strata near both ends 

 of this line, inverted in position, however (like the Longmynd generally), in 

 the northern half. Uriconian volcanic rocks also occurred on the eastern side 

 of the Longuiynd, as at Bagleth. Caradoc, and elsewhere, where, however, 

 they rested transgressively upon the Lower Longmyndian and began with the 

 so-called Helmeth Grits. 



• The Longmyndian formation itself (which was made up of a Lower division 

 of grey, green, and red shales and grits, reminiscent of the Charnian of 

 Leicestershire ; and an Upper division of red sandstones, grits, and conglo- 

 merates, reminiscent of the Torridonian of Scotland, with an intermediate 

 zone — the Bayston Group — combining characteristics of both) was certainly 

 sedimentary throughout. But the materials of which the beds were made up 

 appeared to have been largely pyroclastic in origin, and were often suggestive 

 of simultaneous volcanic action at no great distance outside the Longmyndian 

 area. Broadly speaking, the amount of this ashy or felspathic material in- 

 creased as the succession was ascended, and the typical volcanic rocks of the 

 so-called Uriconian marked apparently the local incoming or culminating 

 phase of this volcanic action, connected perhaps with the movements which 

 brought the Longmyndian to a close and prepared the way for the Cambrian. 



' The igneous rocks of Pontesford Hill, both bedded and intrusive, although 

 perhaps not more varied, were less involved than those of the other Uriconian 

 areas : and now that the Author had so admirably cleared up their character 

 and inter-relations, he hoped that he would carry on his researches into the 

 more complicated Uriconian areas in other parts of Shropshire/ 



The Rev. J. F. Blake said that he had not been able to follow 

 the details so rapidly given by the Author, but he hoped to read 

 them more at leisure. Although he (the speaker) had referred to the 

 relations of Pontesford Hill, he had not attempted any complete 

 account of it, and he would only venture the remark that volcanic 

 tuffs and ashes appeared to him in many cases to be somewhat 

 too freely quoted, considering the difference that they showed when 

 compared with those exposed among recent volcanoes. 



Mr. Parkinson, referring to the great difficulty, from a petro- 

 graphical point of view, of the Pontesford rhyolites, said that he 

 felt that all students of this group of rocks would be grateful to the 

 Author for the able paper which he had submitted to the Society. 



Q. J. G. S. No. 240. . 2 l 



