192 DE. C. E. TILLET Oj* THE PETEOLOGY OF [vol. lxxix, 



junction here is very strong. This junction is seen north of the 

 quarry in the Green Schists. The Devonian slates are altered to 

 brownish iron-stained types, and the junction is marked by an 

 ironstone band hading northwards at a point close to the edge of 

 the quarry plantation. 



Ussher saw fit to class the brown rocks north of this point as of 

 'Green Schist type ; but I am in agreement with Miss Kaisin that 

 these are Devonian, for the typical glossy plryllites can be 

 distinguished in them. These brown rocks have a cleavage-dip 

 northwards, whereas south of the junction the Green Schists dip 

 southwards, forming a syncline. 



In the section at Hall Sands the actual junction is not exposed, 

 but must lie in the small valley between the cliffs at Greenstraight 

 and the cliffs below the chapel. The cliff at Greenstraight con- 

 sists of Devonian rocks which have been stained by iron-oxide near 

 the fault, and correspond to the brown rocks in the Southpool- 

 Creek section. These beds dip consistently northwards, and are 

 followed by the normal Devonian slates. 



Inland, on the north side of the Bickerton valley, a disused 

 •quarry discloses Green Schists, as Somervail first noted. It is 

 clear, as one proceeds eastwards, that the boundary-line is deflected 

 northwards, probably by a transverse fault ; but this cannot be 

 made out on the ground, owing to lack of exposures. In the 

 sections north of Scoble and Ilbertstow Points on the Kingsbridge 

 estuary, the junction-line must lie between slates and mica-schists. 

 The rocks affected by ferruginous solutions are here the mica- 

 schists. 



The remaining junction-section is that exposed along the shore 

 • at Hope village. The junction-rocks here have been intensely 

 affected by the intrusion of quartz-veins. North of the rocky 

 headland well-defined Devonian slates with a northward dipping 

 cleavage crop out on the beach. The junction is exposed in the 

 headland itself : the secondary changes in this case, however, 

 have involved, not only the Devonian strata, but the quartz-mica- 

 schists which form the junction-beds of the southern group. The 

 exact position of the junction cannot be more exactly defined, 

 ■owing to the enormous amount of infiltrated quartz in the form 

 •of veins which has involved both the Devonian rocks and the 

 qtiartz-mica-schists. 



Summing up the evidence yielded by the sections noted above, 

 •one may assert that the metamorphic boundary is well defined. 

 On the north are developed well-cleaved glossy slates, and on the 

 south either Green Schists or mica-schists, which are readily 

 distinguishable from the cleaved slates. Wherever sections can 

 be examined, it can be shown that the rocks at the junction are 

 involved to a greater or less extent in a secondary alteration 

 brought about by ferruginous solutions yielding the so-called 

 '' brown rocks.' These brown rocks may include both members of 

 the Start group or the Devonian slates themselves. At Hope the 

 junction-beds are mica-schists, and the same applies to the section 

 on the Kingsbridge estuary. 



