300 MESSRS. A. HAKKER AND J. E. MARR ON 



cases associated in the same flake. Hornblende and actinolite 

 both occur with the same characters as in the metamorphosed an- 

 desites [1)02 and 875], associated with one another, and in one 

 instance with colourless augite [902] ; but here these minerals are 

 much less abundant than the mica, which is commonly the only 

 ferro-magnesian mineral present in the slides. Hornblende, how- 

 ever, occurs as usual in the metamorphosed vesicles of enclosed 

 andesite-fragments [875]. 



Magnetite is found in octahedra and less perfect forms [796], but 

 it is less abundant than in the metamorphosed andesites, and is 

 often wanting in those specimens most rich in mica [896, etc.], 

 Sphene has not been observed. These facts accord with the sug- 

 gestions offered above ; the titanic acid and most of the iron oxides 

 contained in the rocks have been incorporated in the brown micas. 



The remainder of the rock is a granular aggregate resembling 

 that seen in the metamorphosed andesitic lavas, though not quite so 

 fine-grained. Twinning and twin-lamellation are to be observed 

 between crossed nicols, and it is evident that a large part of the 

 rock consists of reconstituted felspar. This is brought out also by 

 a certain amount of turbidity in the felspars, distinguishing them from 

 the clear quartz, which they sometimes mould. It is noticeable in 

 these metamorphosed andesitic rocks that the originally fragmental 

 examples show signs of subsequent weathering which are not found 

 in the associated lavas„ 



The embedded felspar-crystals have been replaced by an aggregate 

 of new felspar and quartz, with more or less brown mica, and ex- 

 ceptionally a considerable quantity of yellow epidote [900]. In the 

 less metamorphosed examples the original twinning can be vaguely 

 discerned ; in specimens taken close to the granite-junction the 

 structure is totally destroyed, and the pseudomorphs are recognized 

 merely as areas poorer in mica than the surrounding rock. 



The character of the metamorphosed andesitic ashes and agglo- 

 merates is sufficiently indicated by the foregoing remarks. It only 

 remains to be said that there is often a marked laminated structure 

 well indicated by the parallel disposition of the flakes of mica 

 [797, 896], and increasing the general resemblance of these highlj^ 

 altered rocks to true crystalline schists. 



In the thermo-metamorphism of rocks in the vicinity of an igneous 

 mass, it is an important question how far the total chemical com- 

 position has been modified by the changes produced. To give a 

 satisfactory solution of this question would demand a detailed 

 chemical investigation. With respect to the andesitic rocks of 

 Shap Fell, Mr. Garwood has examined for us specimens of highly 

 altered andcsite and ash from near the northern margin of the 

 granite, and finds that they contain only 50*75 and 50-90 per cent, 

 of silica respectively ; i. e. 9 per cent, less than the non-metamor- 

 phosed andesite. This apparent loss of silica is a fact for which 

 we are unable to offer any explanation. There is no strati- 

 graphical reason to suppose that the specimens analysed differed in 

 their original composition from normal augite-an desites such as those 



