﻿Vol. 6 1.] BETWEEN ST. DAVID'S HEAD AND STROMBLE HEAD. 591 



F. Teller and C. von John. 1 It seems advisable to retain this term, 

 for the sake of clearness of description, in order to distinguish rocks 

 which appear to occupy a place between the normal diorites and 

 the norites. Examples of similar gradations from true norites 

 into quartz-bearing rhombic pyroxene -rocks have been described 

 from other localities in addition to the Tyrol ; as, for example, in 

 the Charnockite Series of India, 2 at Ekersund in Norway, 3 and 

 elsewhere. The nomenclature of enstatite-bearing rocks of this 

 type has been a widely-felt difficulty, and has been much discussed 

 by writers on rock-classification. 4 It appears desirable to adopt 

 the term quartz-norite, to include the enstatite-bearing equiva- 

 lent of the quartz-gabbros, in preference to the introduction of a new 

 name, as has been proposed by Mr. J. E. Spurr in describing the sc- 

 called belugite (or norite-diorite) of Alaska. 5 The need for a class- 

 name of this sort is especially felt in cases like the present, in which 

 rocks rich in enstatite are associated with normal diorites wherein 

 rhombic pyroxene becomes distinctly subordinate to hornblende. 



Near the northern flank of Penberry Hill a long, irregular, 

 narrow intrusion extends from Trwyndiallt in an east-north-easterly 

 direction to near Llanvirn. Specimens from this intrusion, taken 

 at Pen Clegyr, show very similar characters to the eastern portion 

 of the Carn-Llidi mass, of which it may possibly be a continuation. 



In the neighbourhood of Portheiddy Common are several thin 

 intrusions, which have a distinctly more basic character. The 

 felspars are in large rectangles, penetrating ophitically now augite, 

 now enstatite. In some parts the latter mineral predominates and 

 occurs in various stages of alteration from an almost unaltered 

 yellowish or colourless variety to the usual fibrous form, but always 

 preceding augite in order of crystallization. Chlorite is fairly 

 abundant. Quartz is practically absent, and apatite is very 

 sparingly represented. The iron-ore is ilmenite, which is not 

 much altered. It would seem that we have here an enstatite - 

 diabase with a tendency to a predominance of enstatite, and 

 differing only from a norite in its ophitic tendency. 



On ascending the hill north of Abereiddy Bay, several other 

 basic dykes are seen along the edge of the cliff. Specimens from 

 these exposures possess very much the same character as those 

 above described, but do not form very satisfactory objects for micro- 

 scopic examination, on account of the large quantity of secondary 

 alteration-products. Despite the confused structure, however, the 



1 'Geologisch-petrograpkische Beitrage zur Kenntniss der dioritischen 

 Gesteine von Klausen in Siidtirol ' Jahrb. d. k.-k. Geol. Reichsanst. 

 vol. xxxii (1882) pp. 589 et seqq. 



2 Mem. Geol. Surv. India, vol. xxviii (1900) pp. 125 et seqq. 



3 J. H. L. Vogt, Zeitschr. fur prakt. Geol. vol. i (1893) p. 4. 



4 See F. Loewinson-Lessing, ' Kritische Beitrage zur Systematik dei* Eruptiv 

 gesteine' Tschermak's Min. & Petr. Mitth. n. s. vol. xxi (1902) p. 311. 



3 ' American Geologist' vol. xxv (1900) p. 233. 



