406 BEPORT— 1888. 



Pentreath (184) almost all the hornblende is gone, and very little epidote 

 is left, and this is in dust-like fragments — the base has crystalHsed into 

 microspectral felspar. The end of this long series could scarcely be more 

 different from the beginning than it is. 



Besides these coarser- grained rocks there is in this district a remark- 

 able series which is schistose in the highest degree. The connection 

 between these and the others is easily traced through a rock just to 

 the south of Y-graig (177), or one at the back of Gaerwen Windmill 

 (174). In the former we have very long and narrow crystals of horn- 

 blende of no definite shape, and small isodiametric crystals of epidote and 

 quartz, and there are also a number of minute brown rutiles. All these 

 are perfectly clean and fresh, and do not appear to have been in any way 

 modified since their formation. In the latter the hornblende has more 

 shred-like ends, the epidote is elongated, and there are only a few minute 

 sphenes. They thus differ only from the former group by their much 

 more marked orientation. It is essentially the same rock as this which 

 occurs in an intrusive form in the Llangaffo cutting. Much of this is 

 highly orientated, though the specimen examined (164) does not show 

 this well, but has larger hornblende crystals, inclosing more or less 

 isolated areas in which there is little but epidote and quartz. From 

 these we pass to a rock at Tyn-drain (167), which agrees with them in 

 every respect, especially with the one at Gaerwen Windmill, except in 

 the replacement of the ordinary hornblende by beautiful blue glaucophane. 

 It contains, however, some scattered elements of speckled felspar and of 

 hornblende, which do not conform to the general orientation. From this, 

 again, it is but a step to the glaucophane schists of the quarry near 

 Anglesey Monument (168, 169), in which that mineral is more pulled out 

 and interfelted, and is in such abundance as to almost play the role of 

 groundmass to the epidote. There is little else than these two in the rock, 

 only a few specks of hematite, and some probably segregation veins of 

 quartz. In the latter float some separated crystals of glaucophane, which 

 may either have been torn from the sides or re-formed with it. The 

 orientation in these rocks cannot be properly called foliation, since it 

 has, at present at least, no relation to a plane, but only to a line — i.e., 

 there is no orientation in a transverse section. Many of these rocks have 

 been examined from various localities, but, with the exception of those 

 that follow, none show any essential difference from the above or 

 peculiarities worth noting. In a rock from near Castellor (172), and 

 another from the south of Newborough (lt'4), there are enclosed small 

 spherical areas, bounded by ferric dust and filled with complex growths 

 of epidote, like the smaller vacuoles figured by Fouquet and Levy in the 

 ' Variolites.' In another rock, near Castellor (171), one of the quartz 

 veins, as already noted, contains small prisms of tourmaline. Like the 

 group with larger crystals, these can undergo still further changes under 

 the action of pressure or stress. Thus, at Carnen Goch (170) the horn- 

 blende is torn out in shreds, the epidote is broken up and elongated, 

 and there are numerous cracks and veins of felspathic and calcitic 

 crystals. Near Holland Arms (176) the lines of orientation are so con- 

 torted and crumpled that they can scarcely be recognised under the 

 microscope, but are evident without it. Finally, at Bryn Gwyn (165) 

 (see fig. 24), and elsewhere on the eastern margin, the elements are so 

 pulled out that they are reduced to little more than dust, and the rock 

 looks little better than an earthy slate. 



