part 2] THE METAMORPHOSED ROCKS OF THE START AREA. 179 



been penetrated by quartz solutions in tbe direction of the major 

 planes of schistosity. Not only quartz-veins, however, but quartz- 

 albite-veins are frequent, some of these reaching a foot in 

 thickness. Albite, often pink- weathered, may predominate almost 

 to the exclusion of quartz. In the Start Schists this veining is 

 -well developed in the coast-sections between Mill Bay and Biddle- 

 head Point, near Dekkler's Point east of Seacombe Sands, and 

 along the coast-sections at Peartree Point, near Start Lighthouse. 



The intimate relation of these rocks with the associated Green 

 Schists is shown by the interbanding near the junction with the 

 latter, and by isolated lenticles of Green Schists enclosed within 

 the main mass of mica-schists. Good examples are afforded at 

 points north of Horseley Cove, below the lighthouse at Start 

 Point, and the bands near the Ferry at Portlemouth, and below 

 Woodville on the opposite shore of the estuary. 



(b) Mica-Schists of the Bolt Area. 



The mica- and quartz-mica-schists of this area are separated 

 'from the group already described by the band of Green Schists 

 stratigraphically interposed. There are no lithological distinc- 

 tions between the two groups such as can be recognized. 



Although the Bolt area is not so continuously accessible as the 

 lower group of mica-schists, yet it is worthy of remark that, in 

 the southern mass extending from Bolt Head to their western 

 limit, no signs of vulcanicity can be observed. The mica-schists 

 are, in the same manner as in the Start group, intimately pene- 

 trated by quartz- and quartz-albite-veins. 



There is a dominant southward dip of the schistosity in the 

 section exposed from South Sands to Bolt Head ; but the absence 

 • of any well-defined lithological horizon prevents detailed deter- 

 anination of structure within the group. 



(c) Petrography. 



Petrographically, the Start and Bolt schists are indistinguish- 

 able ; and in the following petrographic description both groups 

 are included. The mineralogy of these argillaceous sediments is 

 comparatively simple. The principal constituents are quartz and 

 the white mica muscovite, but chlorite and albite may be im- 

 portant members. Accessorily developed are titanite, tourmaline, 

 iron-ores, epidote, zircon, rutile, apatite, and ilmenite. 



Quartz is developed in areas separating bands of muscovite and 

 chlorite. These grains are often distinctly elongated, and are 

 intergrown with a typical sutured texture, sometimes showing 

 undulose extinction. There is thus clear evidence that recrystal- 

 lization in situ is involved. 



Muscovite and chlorite form layers in which these minerals 

 are in intimate association. The chlorite is often noticeably 

 pleochroic, in green to pale yellow-green tints, and may show 



