part 2] THE METAMOEPHOSED EOCKS OF THE START AEEA. 203 



EXPLANATION OP PLATES X & XL 



Plate X. 



Fig. 1. Porphyroblastic albite-epidote-schist, Leek Cove, X 32. The con- 

 stituents are" albite showing inclusions of epidote, chlorite, horn- 

 blende, and sphene. The abundant development of white mica 

 associated with chlorite in parts of this rock shows that it is of 

 tufaceous origin. (See p. 184.) 

 2. Chlorite-epidote-schist, Seacombe Sands, X 32. The constituents are 

 albite, chlorite, epidote, and sphene. Associated with the chlorite 

 are prisms of fibrous amphibole. The analysis of this rock is 

 tabulated on p. 183. 



Plate XL 



Fig. 1. Porphyroblastic hornblende-schist, Prawle Point, X 32. The con- 

 stituents are hornblende in porphyroblasts, albite, epidote, sphene, 

 and a little chlorite. The analysis of this rock is tabulated on p. 186. 

 2. Muscovite-chlorite-garnet-albite-schist, Langerstone Point, X 32. A 

 schist of composite origin. The constituents are white mica, 

 chlorite, almandine-spessartine, albite, quartz, and smaller amounts 

 of epidote and sphene, which appear as inclusions in the garnet 

 (see pp. 189-90). 



Discussion. 



Dr. J. W. Evans expressed his sense of the value of the paper. 

 He was especially interested in the occurrence of albite in both the 

 Green Schists and the quartz-albite-veins. He believed that this 

 was due in both cases to the effects of pressure on the soda-lime- 

 felspars of the local igneous rocks. He thought also that the 

 albitization of the igneous rocks and sedimentaries, which was 

 so marked a feature of North Cornwall, had a similar origin in 

 the pressure-alteration of basic rocks by which the albite of the 

 plagioclase passed into solution, and ultimately modified the 

 composition of other rocks. He was persuaded that the magmas 

 of the alkali- or ' Atlantic ' rocks were also the result of a similar 

 action under enormous pressure beneath the great continental 

 shields. 



Mr. H. Dewey compared the suite of rocks described by the 

 Author with the succession of volcanic rocks in Cornwall. These 

 Cornish rocks include spilites, albite-diabases, minverites, and fre- 

 quently hornblende-picrites, which recur in the Lower Palaeozoic, 

 the Lower Devonian, the Upper Devonian, and the Lower Car- 

 boniferous Series. Their outstanding characteristic is al bite-felspar, 

 which is present in large proportions and apparently as an original 

 constituent. 



The Author had remarked upon the quartz-albite veins of the 

 St;ul area. Such veins are of general occurrence in North Corn- 

 wall among the schistose Upper Devonian sediments and volcanic 

 rocks. The district between Padstow and Trebarwith is marked 

 by an easily recognizable series in which pillow-lavas are but little 

 affected by shearing; but north of Trebarwith the same series 



