A. Market' — Lamprophyres of North of England. 199 



II. — The Lamprophyres of the North op England. 

 By Alfred Harker, M.A., F.G.S., 



Fellow of St. John's College, Cambridge. 



rriHE north-country lamprophyres occur usuallj'' as dykes of no 

 X great magnitude, sometimes as sills, more rarely as small 

 bosses or laccolites. They are scattered over an area extending 

 from Teesdale to Furness, from Bassenthwaite to lugleton. A 

 circle thus defined has a diameter of about fifty miles, and embraces 

 all the known occurrences, though others may exist beyond these 

 limits concealed by post-Silurian strata. In the centre of the circle 

 is the Shap granite, and the probable genetic connexion between 

 the lamprophyres and this granitic intrusion has already been urged 

 by Mr. Marr and the present writer. The chief grounds for such 

 an opinion are as follows : — 



(i.) The arrangement of the intrusions, as just noticed, and the 

 radial grouping of the dykes in the central part of the area about 

 the granite. 



(ii.) The common age of the intrusions, so far as can be fixed ; 

 both granite and lamprophyres being post-Silurian but pre-Carboni- 

 ferous, and both being connected with the same crust-movements. 



(iii.) Certain general chemical relations, to be noticed below ; to 

 which may be added some special chemical characters, such as the 

 notable quantity of manganese in the granite and in most of the 

 dykes analysed. 



(iv.) The special mineralogical resemblance of many of the dykes 

 to the Shap granite, shown by the occurrence in them of charac- 

 teristic minerals such as sphene (rarely found in the lamprophyres 

 of other districts), and especially of the well-known porphyritio 

 felspars of the granite. Some of these points are brought out more 

 strongly by comparing the lamprophyres with the dark basic patches 

 so common in the granite. 



(v.) The arrangement of the different varieties of lamprophyres, 

 the more basic and characteristic ones occurring especially in the 

 outer parts of the area, the more acid varieties and those having 

 most in common with the granite chiefly in the central tract.^ 



(vi.) The close association with the lamprophyres of acid in- 

 trusions of tj'pes more normal for apophyses of granites, and the 

 existence of transitional varieties between these acid rocks and the 

 lamprophyres. 



Many of the individual rocks have been described by different 

 writers,^ and it will be sufficient here to recall some of the more 

 significant characters which they have in common. The typical 



1 It may be remarked here that the lamprophyre of Sale Fell, near Bassenthwaite, 

 which is of a somewhat acid variety, may possibly have had a quite distinct origin. 



'^ Bonney (analyses by Houghton), Q,.J.G.S., vol. xxxv. p. 16o ; Rutley, ibid. 

 vol. xxxiv. p. 29, and Mem. Geol. Surv. Ingleborough (97 S.W.) ; Tate, Proc. 

 Torks. Geol. Pol. Soc. vol. ix. p. 372, vol. xi. p. 311, and Rep. Brit. Assoc, for 1890, 

 p. 814 ; Hatch, ibid. p. 813, and Mem. Geol. Surv. Mallerstang (97 N.W.) ; 

 Balderston. "Naturalist," 1889, p. 131; Harker and Marr, Q.J.G.S., vol. xlvii. 

 p. 285 ; Harker, ibid. p. 521 ; see also Teall, " Brit. Petr." chap. x. 



