Iriii PEOCEEDiN&s of the geological society. 



prevail in the north-eastern parts and run in bands more or less 

 parallel to the leading strata may hereafter furnish fresh data for the 

 decision of this problem : if the rock were originally igneous, these 

 may be the least-changed parts of the deposit ; if it were originally 

 sedimentary, they may be the most- changed parts. 



We may employ the same mode of reasoning for examining the 

 results obtained by Mr. Marshall in treating of the granitic masses 

 of the Lake-district in relation to the undoubted metamorphic strata 

 which surround them. In this tract, as in Cornwall, there is very 

 little gTieiss or mica-schist, except at one or two points, in contact 

 with granite or very near to syenite. The strikes of the strata do 

 not sweep round the granite-bosses ; veins pass from the igneous 

 rocks, and porphyry-dykes emulate the elvan of Cornwall. The 

 granitic masses seldom, if at all, appear to be located on the axis of 

 movement, or to mark out special areas of disturbance (even the 

 granite of the Calder and the syenite of Carrock can hardly be ex- 

 cepted) ; on the contrary, the strikes of the strata run up to them 

 as if to traverse them, and the dips of the strata suffer no special 

 or exceptional derangement at the contact with them. Yet the 

 metamorphism of the rocks which border these granites is very fully 

 manifested, and in such a way as to be continually greater towards 

 the granite, or to some other central space, where, if granite be not 

 visible at the surface, it may, without difficulty, be supposed to exist 

 beneath. 



The explanation offered by Mr. Marshall* of these phsenomena 

 proceeds on the supposition that the strata of the district have been 

 exposed to the action of the general heat of the globe, by reason of 

 the depression to which they have been subjected; that this general 

 heat has been productive of effects varying with the nature of the 

 rock, and graduated by the scale of applied heat, granite being the 

 extreme term of metamorphism, viz. complete fusion, followed by 

 recrystallization. The whole metamorphic tract has been since sub- 

 ject to displacement. 



In some late examinations of a part of this Lake-country, I fol- 

 lowed the footsteps of Sedgwick in the solitary glens of Black Comb, 

 and the metamorphic region on its northern and eastern slopes. In 

 this vicinity we see clearly marked a band of metamorphic green 

 slates, between the Skiddaw slate of Black Comb and the granite 

 and syenite of Eskdale. The metamorphism is various in kind 

 and in degree. The stratification often remains distinct, and is 

 always traceable ; cleavage is traceable ; agate -concretions appear 

 and are elongated in the dip of the cleavage ; some bands of 

 hornblendic rock alternate. On approaching the granite, the masses 

 grow porphyritic ; these greenish porphyries are traversed by 

 syenitic veins, which run along joints and fractures ; parallel to 

 these veins for a very short distance the felspathic base of the 

 porphyry is reddened. Syenitic rocks in mass next appear ; and 

 further on, irregularly, granite diversifies the syenite, and finally 

 appears alone. It is Only in one small narrow ridge near Bootle 



^ See Keport of the British Association for 1858. 



