602 MET AMORPHIC ROCKS OF THE LAKE-DISTRICT. 



7. The volcanic rocks which have as yet been chemically analyzed 

 show a decided increase in the proportion of phosphoric acid on 

 approaching the granite, and a decided decrease in the proportion of 

 carbonic acid. 



Appendix. 



A full list of all papers bearing on this and other geological 

 questions in the district will be found at the end of the official 

 Survey Memoir on the northern part of the Lake-district ; but it will 

 be necessary to mention some of the views of previous authors on 

 the subject of this paper. 



Prof. Sedgwick, in his letters on the Geology of the Lake-district, 

 dated 1842, speaks of the zone of altered rocks around the Eskdale 

 granite, "which forms such a passage between the two formations 

 that it is no easy matter to determine the exact boundary-line of 

 either." 



Prof. Phillips, in 1858,* alludes to the great series of changes in 

 the volcanic rocks around the granite near Bootle. 



Mr. J. G. Marshall, in the same year and in 1861 states t his 

 conviction that the granites and syenites are truly metamorphic, he 

 does not, however, regard the green slates and porphyries as volca- 

 nic, but considers that " the vjhole series were originally soft stratified 

 deposits." In a paper, dated 1868 $', Dr. Nicholson draws the 

 following general conclusions — that the Shap granite is of hydro- 

 igneous origin, and that neither it nor the other granites of the dis- 

 trict are in any way connected with axes of elevation or disturbance. 



EXPLANATION OF PLATE XXXI. 



To illustrate the microscopic structure of granitoid rocks, and the passage 

 from altered volcanic rocks to granite. 



Fig. 1. Altered ash, with lines of bedding seen in the mass, from south-west of 

 Bell Rib, Yewbarrow, above Wastwater. Magnified 50 times. 



2. Altered contemporaneous trap (?), close to the Wastdale Head granite, 



Lingmell Beck. Magnified 50 times. 



3. Represents the same field of view as that seen in fig. 2, but in polarized 



light, with the prisms crossed. Magnified 50 times. 



4. Highly altered ash, close to the Eskdale granite, west of Great How. 



Magnified 50 times. 



5. Bastard granite, traces of bedding in the original ash rock still visible 



on the weathered exterior, Peers Gill (below Flass Knotts), foot of 

 Scawfell Pikes. Magnified 50 times. 



6. Eskdale granite, at the edge, south of Great How. Magnified 50 times. 



7. Junction of highly altered ash with Shap granite, Sleddale Pike. Magni- 



fied 25 times. 

 These figures have been copied from coloured drawings made by the author 

 direct from the microscope. 



* " Notice of some phenomena at the junction of the granite and schistose rocks 

 in W. Cumberland," Rep. Brit. Assoc. 1858, Trans. Sects, p. 100. 



t " On the Geology of the Lake District, in reference especially to the Meta- 

 morphic and Igneous rocks," Brit. Assoc. Rep. for 1858. Trans. Sects, p. 84, and 

 1861, p. 117. 



\ " On the granite of Shap," Trans. Edin. Geol. Soc. vol. i. p. 133. 



