METAMORPHISM IN SOUTH DEVON. 381 



as earth-movements might produce. The age of these schists is un- 

 certain, but they present a close resemblance to the micaceous and 

 chloritic schists of Anglesea and Holyhead, and they have similarly 

 been grouped with the Archaean series. 1 



Schists of South. Devon. The rocks of South Devon between 

 Start Point and Bolt Tail are highly metamorphosed. They consist 

 to a large extent of mica schist, though in many places this rock gives 

 place to chloritic schist, as at Prawle Point and in Bolt Tail itself, 

 and on the east side of Salcombe estuary. This region has always 

 appeared interesting because Sir Henry De la Beche was inclined to 

 regard it as indicating progressive metamorphic action, which increased 

 in intensity southward, while Sedgwick and Murchison inclined to 

 the belief that the southern schists show no transition to the northern 

 slates. Their views have been confirmed by Professor Bonney, who 

 finds that there is a passage from slates and phyllites to rocks with 

 incipient metamorphism into schists, which is too rapid to indicate 

 transition. This author observes concerning the mica schists that in 

 some cases the structure of the crystalline constituents indicates that 

 folding has been the first stage in the process of metamorphism, 

 and that the chemical or mineral change has been subsequent to the 

 mechanical one. In other cases the folding and crystalline changes 

 appear to have been produced together, while in a third case the rock 

 was crystalline before it was folded. Professor Bonney arrives at 

 the conclusion that the metamorphism was long anterior in date to 

 the great lateral compression which has corrugated the rocks. Dr. 

 Holl regarded the slates at Tor Cross as newer than the Plymouth 

 Limestone, but Professor Bonney thinks that the Cornish metamor- 

 phic rocks suggest that these may be a prolongation of the schists of 

 the Lizard, which may have included the gneiss of the Eddystone, and 

 that they too date back to the Archaean period. 2 



Metamorphic Rocks of Anglesea. Anglesea exhibits schists in 

 grand development. North of the Holyhead Road they are green 

 an,d purple, and often micaceous, and lie in wavy lamination. North 

 of Church Bay they are a white or yellow felspathic schist; and 

 between Carmel's Point and Church Bay gneiss is well developed, 

 and the bedding has so entirely disappeared that the rocks have the 

 aspect of igneous masses. In this part of Anglesea the bedding and 

 foliation cross each other. Holyhead Island is formed of gnarled 

 schists, in which stratification, foliation, and cleavage are frequently 

 indistinguishable. Nowhere are the strata more violently contorted 

 than in the cliffs and islets round Holyhead. The eastern half of 

 Holyhead is described by Sir Andrew Ramsay as a kind of quartz rock. 

 Professor T. M'Hughes indicates four great masses of gnarled schists, 

 the Holyhead mass, the Amlwch mass, the Llangefui mass, and the 

 Menai mass. 3 



Foliation in the Volcanic Series of St. Davids. Professor A. 

 Geikie remarks that a fine foliation, arising from the development of 



1 Bonney, Q. J. G. S., vol. xxxix. p. i. 2 Q. J. G. S., vol. xl. p. i. 



3 Q. J. G. S., vol. xxxvi. 



