THE SHAP GRANITE AND ASSOCIATED ROCKS. 301 



of Stockdale, but they probably do not occupy quite the same 

 horizon. 



Thermo-metamorphism in andesitic rocks has hitherto received 

 but little attention. Prof. Judd * has adverted very briefly to some 

 changes of this kind in the andesites or " propylites " of the 

 Western Isles of Scotland. He alludes to the formation in the 

 contact-zones of colourless secondary pyroxene, magnetite, and deep 

 brown biotite, with possibly melilite and felspar ; but we do not 

 gather that these phenomena are exhibited on any extensive scale. 

 As regards the metamorphism by heat of augitic rocks in general, 

 the first important record is that of Mr. AUport f, who showed that 

 in the neighbourhood of the Cornish granites the augite of the 

 ^' greenstones " has been replaced by hornblende and actinolite. It 

 appears from his description, and from the only Cornish examples 

 we have examined, that there, as in the Shap Pell andesites, much 

 at least of the augite must have been converted into secondary 

 minerals before the metamorphism [1129]. Prof. Lessen J, however, 

 describes appearances in the metamorphosed diabases in the Harz, 

 which leave no doubt as to the direct " uralitization " of augite under 

 the influence of a granitic intrusion ; and a series of slides from 

 specimens taken near Rosstrappe, Thale, one of his typical localities, 

 show that hornblende has been formed both directly from augite 

 and also from its decomposition-products [469-473]. The ofiicers 

 of the Geological Survey of Saxony § have described the conversion 

 of diabases into actinolite- and anthophyllite-schists around the 

 syenite of Meissen. 



B. The Bhyolitic Bocks. 



The rhyolites of the district, whether associated with or underlying 

 the Coniston Limestone, have characters familiar to geologists who 

 are acquainted with Ordovician volcanic rocks in other parts of- 

 Britain, and we do not propose to enter into many details with 

 respect to their general features. Moreover, owing to their com- 

 paratively simple chemical and mineralogical constitution, they do 

 not present such diversities in their modes of metamorphism as have 

 been described in the case of the andesites. In the field, indeed, the 

 rhyolites seem to show little or no change, as they are traced along 

 their strike into the aureole of metamorphism ; but this idea is 

 dispelled by a closer study of the specimens. 



At a distance from the granite, the rhyolites may be studied in 

 Stockdale and Long Sleddale. They often have a grey colour with 

 a rather flinty appearance ; when this is wanting, they are pink or 

 cream-coloured, but always of compact texture. One type is lami- 

 nated parallel to its flow-lines, and often has a fissile structure in 



* Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 370. 

 t Ibid. vol. xxxii. (1876) p. 418. 



t ' Erlaut. zur geol. Specialk. Preuss.,' Blatt Harzgerode (1882), pp. 79, &c. 

 § ' Erlaut. zur Specialk. d. Konigr. Sachsen ' (1889), K. Dalmar, Section 

 Tanneberg, Blatt 64 ; A. Sauer, Section Meissen, Blatt 48. 



