200 



plane of schistosity. In the latter case they are frequently associated with 

 small granules of colourless sphene. 



The distribution of the foliated and non-foliated rocks in the dyke is 

 sometimes extremely irregular and quite independent of the course of the 

 dyke ; at other times the foliation exhibits a marked tendency to curve 

 round so as to become parallel with the margins. 



There seems no reason to doubt that the change of the plagioclase- 

 pyroxene rock to epidiorite and hornblende-schist is the result of the 

 dynamic metamorphism which has affected the district. Where there has 

 been no differential movement in the rock-mass we have the massive epi- 

 diorite ; where differential movement has taken place the schist has been 

 produced. Why certain portions of the dyke have retained their original 

 characters, whilst other portions have been so completely metamorphosed, we 

 cannot at present explain. Many dykes similar to that of Scourie doubtless 

 occur in the Highlands of Scotland, and it is quite possible that many 

 bands of hornblende-schist may represent dykes or sheets which have been 

 incorporated, as it were, in the general gneissic series. 



I. II. 



Si0 3 .. 47-45 ... 49-78 



Ti0 2 ... 1-47 ... 2-22 



A1 2 S ... 14-88 ... 13-13 



Fe 2 8 ... 2-47 ... 4'35 



FeO ... 14-71 11-71 



CaO ... 8-87 ... 8-92 



MgO ... 5-00 ... 5-40 



K 2 ... -99 ... 1-05 



Na 2 ... 2.97 .... 2-39 



H 2 ... 1-00 ... 1-14 



CO, -36 -10 



10012 100-19 



Sp. Gr. .. 3.10 3-11 



I. Bulk analysis of the plagioclase -pyroxene rock. Dyke, Scourie (TEALL). 

 II. Bulk analysis of the hornblende schist (TEALL). 



North of England. The dykes in the North of England are mostly 

 found in the districts occupied by Carboniferous rocks. One only, viz. 

 that of Cleveland, occurs in conjunction with Secondary strata. As this 

 dyke cuts the highest Jurassic strata in the district through which it 

 passes, and produces marked contact alteration, there can be little doubt 

 that it is of Tertiary age. It has been followed at intervals for a 

 distance of ninety miles. A detailed examination of this dyke at many 

 points along its course has established the fact that it is remarkably 

 constant in composition; a feature which it possesses in common with all 

 the other dykes of the North of England. It is porphyritic in texture ; 

 the porphyritic character being determined by tabular crystals of labra- 



1). TEALL. Petrological Notes on some North of England Dykes. Q,J.G,S. Vol, XL, 1884, p. 209, 



