534 THE MELAPHYRE8 AND FELSITES OF CARADOC. 



29. On some of the Mblaphiebs of Caradoc, witJi Notes on the 

 Associated Felsites. By Frank Huxley, Esq., F.G.S., Lecturer 

 on Mineralogy in the Royal College of Science, London. 

 (Read June 24, 1891.) 



[Plate XIX.] 



Contents. 



Page 



I. Introduction 534 



II. The Melaphyre Series 534 



III. Conclusions with regard to the Melaphyres 539 



IV. The Felsitic Series 540 



V. Conclusions with regard to the Felsites 542 



VI. Supplementary Note 543 



I. Ixtroduction. 



While staying at Church Stretton during the autumn of last year 

 I paid several visits to Caradoc Hill for the purpose of acquiring 

 some information concerning the nature of the felsites which occur 

 there. Many chips were collected, not only of felsites but also of 

 basic eruptive rocks, and sections were subsequently cut from those 

 specimens which seemed likely to show points of interest. 



Although the structural geology of this area has been investigated 

 by several observers since the publication of the Geological-Survey 

 map, no account of the microscopic characters of these rocks appears, 

 hitherto, to have been published. In the following paper an attempt 

 is made to supply this deficiency to a certain extent, but, since the 

 time at my disposal permitted the collection of specimens from only 

 a limited portion of Caradoc Hill, chiefly from diff'erent spots situated 

 to the south and south-west of the Camp, there remains much ground 

 which the present paper leaves untouched. 



The points from which the different specimens were derived are 

 marked with some approximation to truth on the accompanying 

 outline map, on which the geological boundaries laid down on the 

 published Survey map are indicated. The Arabic numerals refer to 

 the numbers with which the specimens of felsite, derived from 

 those spots, were ticketed, while the Roman numerals denote basic 

 eruptive rocks. The numbering of the specimens and sections 

 bears no relation to any sequence in the field or relation of the 

 rocks to one another, and has merely been retained to avoid any 

 possible source of error from re -labelling. 



II. The Melaphyre Series. 



The following are descriptions of certain selected types of the 

 Melaphyre Series. 



No. XII. S.W. side of Caer Caradoc, near the top of the hill. 

 Altered vesicular basalt-glass. (Melaphyre.) 



