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



apparently a pseiulouioipli after pyrites, as the latter mineral Las 

 not been noticed in either of my nine slides of these quartz-schists, 

 whereas red iron oxides are abundant. 



Black granules and streaks, ajjparently magnetite, occur in all 

 the above four slides, but as they in no instance exhibit the 

 characteristic octahedral ci-j'stallization of that mineral, their evidence 

 is only of minor importance. It is well worthy of notice that in 

 three of these four slides, two being from the metamorphic district, 

 and one from outside the boundai-y, we have pyrites intimately 

 associated with hfematite, either in the same crystal, or as a pseudo- 

 morph ; and further, that on either side of the boundary we find 

 pyrites crystallized in the somewhat uncommon form of rect- 

 angular prisms. 



Tourmaline. 



Tourmaline has been noticed in ten slides from the following six 

 Devonian localities, viz. quarry near Kilmorie, Torbay ; north-east 

 end of Slapton Sands; cliffs south of Beesands ; grit band in Southpool 

 Creek ; near East Charleton ; and Aveton Giffard : and in eight slides 

 from two bands of quartz-schist on the coast south of Start Farm, in 

 the metamorphic area. In every case the larger grains are clearly of 

 detrital origin, the only exception being in one or two instances in 

 the quartz-schist, where secondary tourmaline has crystallized on 

 the original grains, and these secondary crystals have been swept to 

 a distance by differential movements in the rock.' 



No alteration by pressure or solution has been observed in the 

 tourmaline grains in rocks north of Beesands, the first indication 

 noticed being south of that village. 



In a reddish grit containing much hsematite (No. 59), a well- 

 characterized light-brown crystal of tourmaline is broken sharply in 

 two, and slightly dislocated. Clear quartz fills the intervening gap 

 without in the least dissolving the edges of the tourmaline cr^'stal.^ 



A grain of tourmaline in another slide from the same neighbour- 

 hood (No. 5) is slightly, albeit distinctly, affected by solution, with 

 indications of the re-crystallization of secondary tourmaline. 



In a slice (No. 16) of one of the quartz-schist bands south of 

 Start Farm, two crystals of tourmaline may be especially noticed : 

 one, a longitudinal section, with characteristic transverse cracks ; the 

 other a basal section. In each case there is a considerable gi'owth 

 of secondary tourmaline on the original crystals ; and in each case 

 also, by a slight differential movement of the rock, fragments of 

 this secondary tourmaline have been detached and moved to a small 

 distance from the parent crystal. 



We have thus close together in the same field of view detrital 

 tourmaline and induced tourmaline.^ The origin of the latter would 

 be obscure, were not all the steps of the process so clearly set forth. 

 Tourmaline occurs in many torujs and colours ; but the tourmalines 

 of Beesands and the Start coast are identical. 



1 Plate VI. Y\g. 2. "- Plate YI. FIr. 1. ^ Plate VI. Fig. 2. 



