Yol. 57.] IGNEOUS SOCKS OF THE TORT WORTH INLIER. 279 



Pig. 3. — Section acmss Middle Mill (Horsley) Qaarry. 

 N.W. F S.E. 



Scale: I inch = 30 yards. 



Sandy limestone (Upper Llan- 

 dovery) with lapilli. 



T = Compact trap ; T*=: Crushed trap. 

 FF= Faults. 



III. The Petrology of the Igneous Eocks. 



With regard to the nature of the igneous rock, Weaver describes 

 it as a granular and compact greenstone, sometimes, though rarely, 

 graduating into basalt, with occasionally disseminated portions of 

 hornblende or augite, with granular and compact felspar, claystone, 

 and amygdaloid. Buckland & Conybeare speak of it as ' amyg- 

 'daloidal trap ' ; Stoddart, who gives analyses, one of which shows 

 10 per cent, of potassium oxide (!), as 'greenstone'; Phillips, as 

 varying from an ordinary close-grained greenstone to largely 

 vesicular amygdaloid. Mr. Rutley, in an appendix to Mr. H. B. 

 Woodward's Geological Survey Memoir, gives a fuller and more 

 careful description, based on the microscopic examination of sections. 

 He notes the occurrence of olivine in a specimen from Charfield 

 Green, and describes the rock as essentially a basalt. The rock from 

 Damery he describes as a dark, brownish-grey, compact basalt, and 

 notes the occurrence of plagioclase with twin-striation, of augite 

 altered to a serpentinous material, and of magnetite. Mr. J. J. H. 

 Teall's description of the Damery rock will be quoted under (c) 

 (p. 281). 



In our examination of these rocks we have been much helped by 

 Mr. J. Parsons, B.Sc, who has determined the silica and alkali- 

 percentages which we quote, and has supplied us with notes on 

 certain points connected with the microscopical observation of some 

 of the rocks. Our colleague, Mr. E. B. Ludlam, has kindly deter- 

 mined the specific gravities. 



(a) The Charfi eld-Green Exposures. 



(1) The easterly or lower band. — Behind the cottage by 

 the stream, 300 yards south-east of Charfield-Green station, is an 

 exposure of a reddish-brown, fairly fresh, non-amygdaloidal rock, 

 which has a specific gravity of 2*74, and on analysis yielded the 

 following percentages :— SiO, 58-55; Kfi 1-81 ; Na,0 2-98. 



Mr. Parsons remarks on the extremely hydrous character of the 



