246 A. R. Sunt — Devonian Hocks of S. Devon, 



to <i:o no further a-field than the coast-line. Both the sandstones 

 and quartz-schists contain mica varying between the minutest filmy 

 flake, hardly seen in the microscope, and flakes sufiiciently apparent 

 to the naked eye. Given a small amount of solution in the silica 

 of the quartz-grains, so that the mica flakes might be free to partially 

 rearrange themselves, and there seems to be no reason why the 

 Start quartz-schist under consideration should not have been derived 

 directly from such a rock as the Kilmorie sandstone, without any 

 development of newly-formed mica. 



So far as I understand it, a theory held by some is that the 

 Devonian slates and sandstones when micaceous are with very few 

 exceptions " Phyllites," in which the mica is considered to be an 

 induced product ; and that the mica-schists are rocks in which the 

 mica has also been induced but to an incomparably greater extent, 

 so that the rocks differ in kind. It seems, however, possible, that 

 the converse of this may be true, and that with some exceptions 

 the mica in both the Devonian and metamorphic rocks is, or was, 

 originally, detrital, the deposition of micaceous sediment being much 

 more general in the southern area than further north. Irregular 

 deposition is occasionally exemplified in the Torbay rocks, in which 

 worm-tracks in slates are filled with fine micaceous silt. 



In the foregoing pages the iron ores, tourmaline, micas, and 

 quartz-grains of the Devonian sandstones have been connected with 

 the iron ores, tourmaline, micas, and quartz-grains of the meta- 

 morphic quartz-schists. It cannot be doubted that were the rocks 

 further examined by a competent mineralogist, other points of re- 

 semblance would be noticed, for minute grains of felspar, unless 

 well defined, and the rarer minerals, are beyond the power of my 

 microscope and knowledge to distinguish. 



One noticeable feature which the grits and quartz-schists possess 

 in common is the abundance of laminae of iron oxides : at Hope's 

 Isose, black ; at Kilmorie, brown ; at Slapton Sands, red ; at Bee- 

 sands, black and red ; at the Start, black and red. The colours 

 being probably due to the brown, red, and black, oxides of iron. 

 The following remark of M. Daubree is worth noticing, although 

 the black oxides of the Start schists do not take the form of 

 crystallized magnetite : — 



''Dans certaines localites des Ardennes, les cristaux de fer oxy- 

 dule, qui impregnent les ardoises se sont loges suivant les longrains, 

 et font ainsi ressortir des joints rudimentaires qui, ailleurs, ne sont 

 pas reconnaissables a la vue." — Geol. Experimentale, vol. i. p. 336. 



At the Start we find the quartz-schist traversed by numerous 

 little cracks cemented by opaque iron-ores. 



The Mica-Schists and Slates. 



The mica-schists of the metamorphic district, as distinguished from 

 the schists in which quartz is the most prominent mineral, have not 

 been examined to any extent. 



One specimen of a red schist, which I thought might compare 

 with the red Devonian slates, is described by Mr. Barker as a rook 



