288 MESSRS. A. HAEKER AND J. E. JIARR ON 



type of " mica-traps " found at greater distances from the 8hap Fell 

 intrusion. For instance, the rounded quartz-blebs, which are found 

 in all the Stakeley Folds rocks, occur occasionally in mica-trapa as 

 far away as Swindale, near Knock, 14 miles from the granite, 

 although there the groundmass contains no original quartz. The 

 Swindale intrusions, too, have here and there a crystal of felspar, 

 either of the red or of the colourless glassy-looking kind, the edges 

 showing the rounding already noted in our rocks. The " glomero- 

 porphyritic " clusters of small felspars have been noticed by Mr. 

 Tate * in one of the Ingleton dykes. At the same time, the special 

 characters of the Stakeley Folds rocks are met with more rarely at 

 greater distances from the Shap Fell granite. From Prof, lionney's 

 descriptions we gather that of the seventeen dykes examined by 

 him (at distances of 5 to 14 miles from the granite), only one had 

 original quartz-grains, and he adds that " their appearance suggests 

 the possibility of their having been caught up by the molten rock." 



We do not find in published descriptions anything to compare at 

 all closely with the above group of intrusions as a whole. It may 

 be worth noting that the well-known " porphyroide " of Mairus in 

 the Ardennes, described by MM. de la Vallee Poussin and lienard f, 

 is a biotite-quartz-porphyry in which the porphyritic felspars show 

 phenomena of rounding and bordering in some respects similar to 

 those noticed above. 



The largest dyke in this part of the district is one exposed on 

 the moorland some four or five hundred yards south of Wasdale Old 

 Bridge. It strikes in a nearly N.W.-S.E. direction, and is remark- 

 able for containing porphyritic crystals of monoclinic felspar (in 

 the form of partially-interpenetrating Carlsbad twins nearly two 

 inches long). It has also porphyritic quartz in good crystals u]) to 

 -V inch, showing prism- as well as pyramid-faces ; and these occur 

 in great numbers enclosed in the large felspars, as well as in the 

 general mass of the rock. The felspars have a very pronounced 

 tabular habit, parallel to the clinopinacoid, the thickness of a 

 crystal being less than one-fifth of its length. The forms present 

 are the usual clinopinacoid, prism, basal, and hemidome, with 

 another form {h Jc I) not determinable on the specimens. The 

 mineral has a strong glassy lustre, and the third cleavage (parallel 

 to the orthopinacoid) is well developed. These characters, with the 

 tabular habit, are the chief mineralogical grounds on which sanidinc 

 is usually separated from orthoclase, and there seems to be no 

 reason why these crystals should not be named " sanidine." 



A numijer of other dykes, showing in some degree a radial 

 arrangement about the granite, are marked on the Geological 

 Survey map, and we have examined several of these between Shap 

 Fell and Tebay, and farther west and south. In many cases the 

 rocks are deeply weathered, and detailed descriptions would not be 

 very profitable. It is sufficient to note that some are ordinary 

 quartz- por[)hyrics ; others are normal mica-traps with no original 



* Brit. Assoc. Kep. 1890 (Leeds Meeting), p. 814. 

 t Mem. couronn. Acad. Roy. Brux. (1876). 



