496 ME. B. HOBSON ON THE BASALTS AND 



36. On the Basalts and Andesites of Devonshire, known as 

 ' Felspathic Teaps.' By Beenaeb Hobson, Esq., M.Sc, P.G.S.^ 

 Lecturer in Geology in the Yictoria University,. Owens College, 

 Manchester. (Read June 22nd, 1892.) 



Contents. 



Page 



T. Previous Literature 496 



II. Evidence of the Contemporaneous (non-Intrusive) Character of the 



Eocks 497 



III. ImprobabiHty of the Former Existence of these Lavas in the Area of 



the Dartmoor Granite 498 



IV. Intrusive Dykes in supposed New Eed Trap near Plymouth 499 



V. Other alleged Intrusive Dykes in the Lavas 500 



VI. List of Localities examined , 501 



VII. Maeroscopical and Microscopical Characters of the Rocks 502 



(a) Olivine-basalts. 



(6) Quartz Inclusions. 



(c) Mica-augite-andesite of Killerton. 



I. Peevious Liteeattjee. 



1797. W. G. Maton. Observations relative chiefly to the Natural 

 History, Picturesque Scenery, and Antiquities of the "Western 

 Counties of England. Salisbury, vol. i. pp. 95-97 (describes the 

 Thorverton stone). 



1811. J. F. Berger. Observations on the Physical Structure of 

 Devonshire and Cornwall. Trans. Geol. Soc. vol. i. pp. 100-102 

 (describes the amygdaloid of Poucham [probably Pocombe], Dpton 

 Pyne,^ and Thorverton). 



1821. Rev. J. J. Conybeare. On the Geology of the neighbour- 

 hood of Okehampton, Devon ("memoranda on the Red Marie '' at 

 end) ; Annals of Philosophy, new series, vol. ii. pp. 165, 166 

 (describes the amygdaloid of Thorverton, Silverton, and Radden 

 [Raddon Court] quarries). 



1835. Sir H. T. De la Beche. " Note on the Trappean Rocks 

 associated with the (New) Red Sandstone of Devonshire," Proc. 

 Geol. Soc. vol. ii. (1833-8) pp. 196-8 (mentions the trappean rocks 

 " near Tiverton, Thorverton, Silverton, KeUerton Park, Crediton, and 

 Exeter," and gives the geological history of those at "Washfield, near 

 Tiverton. 



1839. Sir H. T. De la Beche. Report on the Geology of Cornwall, 

 Devon, and West Somerset (Geol. Survey Memoir) pp. 199-204, 

 211, 212, 215, 216, 489. 



1839 ? (no date). One-inch Geological Survey Maps, Sheets 21, 

 22, 24, 26 (almost all the important exposures are included in 

 Sheets 21 and 22). 



^ Later observers do not mention Upton Pyne. I have not visited the 

 locality. 



