292 A. R. Hunt — Devonian Rocks of South Devon. 



I have specimens of felspar veins or infiltrations, from Start Farm, 

 Lannacomioe Mill, West Prawle, Kickham Sands, Starrall Bottom, 

 South Down, and Bolbury Down, thus covering the area of the mica 

 and quartz schists nearly from sea to sea. This felspar constitutes 

 an important, even though it be a minor feature, in the petrology of 

 the district. 



Veins of felspar, quartz, and chlorite, in association, are not, I 

 believe, common in the Devonian sedimentary rocks : the only 

 locality in which they occur to my own knowledge being on the 

 raised beach platform at Compass Cove outside Dartmouth Harbour, 

 where Devonian sedimentary rocks are in close proximity to dia- 

 bases both north and south. ^ Here quartz is the predominant 

 mineral, with felspar sparingly intermingled and chlorite still more so. 



Sir Henry de la Beche described the Eddy stone reef as "a variety 

 of gneiss similar to some occurring near the Prawle Point." '^ Had 

 the veteran geologist written ' West Prawle ' or ' East Prawle,' 

 instead of ' the Prawle Point,' there would be little difficulty in the 

 case, as whereas the Prawle Point is in the area of the Green Rocks, 

 the two villages of that name are on the mica-schists. The Eddy- 

 stone gneiss has many points in common with the felspathic mica- 

 schists, but very few with the Green Kocks. For instance in a slide of 

 mica-schist from near the Bolt Signal Station we find quartz with 

 minute bubbles, white mica, felspar, chlorite, and garnet. All these 

 minerals reappear in the Eddystone gneiss, with brown mica in 

 addition. All slaty structure has completely vanished, but I scarcely 

 think the Eddystone is more in advance of the Bolt, than the Bolt is 

 ahead of the Start, and the Start of the Devonian micaceous sand- 

 stones of Beesands. 



Besides the points of general resemblance between the gneiss of 

 the Eddystone and the mica-schist of the Bolt district, it is interest- 

 ing to note that felspar- quartz veins with chlorite also occur in the 

 Eddystone rock, and were described by Mr. Tawney in 1881.^ 



Two authors have noticed the green decomposition-products of 

 the South Devon greenstones. In 1888 Mr. A. Somervail incidentally 

 observed that both the diabases and green schists were charged with 

 epidotic and chloritic minerals.* In 1889 Miss C. A. Raisin demur- 

 ring to this statement, so far as it affected the diabases, said, that in 

 them she had found chlorite to be "generally rare and often absent ; "^ 

 but records viridite in two specimens, and a variety of palagonite 

 in a third. Further, the authoress distinguishes between the " well- 

 defined " chlorite of the southern rocks and the green mineral of the 

 diabases. 



After a careful examination of 28 slides of the schists and diabases 

 I find that 14 out of 16 of the latter contain, in greater or less 

 quantity a pale-green mineral which seems to correspond with 

 Professor Rosenbusch's description of chlorite. 



1 Since the above was in type I have been indebted to Mr. TJssher for excellent 

 specimens from the neighbourhood of Banthara. 



* Rep. Dev. and Cornwall, p. 32. •* Trans. Dev. Assoc, vol. xiii. p. 172. 



* Trans. Devon. Assoc. 1888, p. 224. A rock from Redlap, in Mr. Somervail's 

 collection, is crowded with macroscopic crystals of typical epidote, associated with 

 a little chlorite. * Geol. Mag. 1889, p. 266. 



