A HISTORY OF DEVONSHIRE 



IGNEOUS ROCKS IN THE PALAEOZOIC AREA 



The igneous rocks in the Palasozoic area may be divided into four 

 classes : the contemporaneous volcanic rocks, rocks which may be 

 either contemporaneous or intrusive, intrusive greenstones, intrusive 



felsites. 



The first two classes are confined to south Devon. 



There can be no doubt that many of the sheared rocks in the 

 Dartmouth slates are contemporaneous ; of this class a rhyolitic felsite at 

 the south end of Blackpool Sands (near Stoke Fleming) and an amygda- 

 loidal diabase at Muxham Point (Erme Mouth), both displaying well 

 marked fluxion structure, are examples. In the Meadfoot group the 

 Torcross type (apparently a modified diabase) is often of doubtful origin, 

 but diabase porphyrite quarried south of East Charleton and many of the 

 sheared bands in the Kingsbridge creeks and elsewhere are evidently 

 contemporaneous. In the Middle Devonian and Upper Devonian 

 (more locally) the contemporaneous rocks include tuffs, shalsteins, 

 amygdaloidal and slaty diabase, or diabase tuffs. In the Ashton and 

 Tavistock districts there are also volcanic rocks in the Lower Culm. 

 Near Devonport Workhouse and south-east of Plympton there are ex- 

 amples of intrusive and contemporaneous basalts. Intrusive Greenstones 

 are very numerous especially in the Middle and Upper Devonian, and in 

 the Lower Culm locally, but the possibility of some of them being con- 

 temporaneous volcanic rocks must be admitted. 



Examples of epidiorite occur among altered Lower Culm rocks on 

 Cox Tor near Tavistock, east of Canonteign and south-west of Bagtor in 

 the Chudleigh area. 



Dolerites may be seen in the Middle Devonian in Borough quarry 

 (west-north-west of Denbury), Yarner Beacon near Dartington, in the 

 Lower Devonian at Capton near Morleigh ; ophitic dolerite in Lower 

 Culm, north of Place Barton (near Ashton), south of Christow ; in Upper 

 Devonian on Knowles Hill (Newton Abbot) ; in Middle Devonian near 

 Lower Ware (Kingsteignton) and south of Dittisham corn mill, etc. 



Leucophyre. — In Lower Culm east of Huish near Hennock, and 

 railway cutting north of Ashton., 



Diorite. — In Lower Culm south of Standcombe farm near Bick- 

 ington. 



Porphyritic diabase. — Dunhill quarry south of Brent, very common 

 in Middle Devonian. 



Aphanite is also very common in the Middle Devonian. Granular 

 diabase is met with in Middle and Upper Devonian. An example occurs 

 at Carey Arms (Babbacombe) . 



At Fremington Pill in north Devon in the Lower Culm there is a 

 dyke of highly altered basalt (specimen identified by Teall). 



Dr. Busz * classes the Botter Rock near Hennock with the leuco- 

 phyres. He also notes a Labrador porphyry allied to the leucophyres 



• Sifz d. Niederrhelnische Gesell. im Bonn. 1893, p. 83. 

 24 



