202 



Mr. S. Allport and Prof. T. G. Bonney. [June 6, 



towards it. Both are slightly foliated. One (not sliced) is the ordi- 

 nary finely granular quartz-mica rock, but having some thin pale- 

 green laminoe ; the other, in which the greener bands predominate, 

 occurs about 5 yards above it. In the slide there is very little 

 brown mica, the pyroxenic constituent predominating. Most of this 

 is hornblende, but some may be the augite already described. There 

 is a little of what seems to be dirty calcite, and a few grains which 

 may be either an impure epidote or possibly sphene. Rock frag- 

 ments cannot be distinguished ; probably the rock was originally a 

 rather fine-grained earthy grit. Occasionally the pyroxenic minerals 

 lie with their longer axes at a high angle with the general foliation 

 of the rock. 



The remaining specimens (422, 423) are from near a bridge over 

 the Ken, about 1tt miles from the nearest visible granite, and on the 

 line of strike of the last named. The macroscopic aspect of the one 

 is perplexing. In some respects it resembles an ordinary, fairly 

 coarse mica-schist, rather crushed out and cleaved ; in some a schistose 

 micaceous grit ; while in some it recalls the specimens above 

 described. In any case it evidently has been affected by pressure. 

 Microscopic examination discloses a distinctly fragmental structure, 

 but in addition some mineral change. The rock mainly consists of 

 grains and granules of quartz, and of flakes of mica of every tint, 

 from almost white to olive-brown, and of variable dichroism, with 

 earthy grains and specks indicating the presence of iron oxides and of 

 an aluminous mineral ; a few better preserved fragments are also 

 present, which are almost certainly more or less altered felspar.* 

 There is a little recognisable epidote, and one or two small zircons. 

 The quartz is no doubt in parr- secondary, but the larger grains have 

 a distinctly fragmental aspect; these occasionally measure about 

 O'Oo" in their longer diameter, but commonly not more than - 01". 

 Sometimes the boundary is fairly sharply defined, but generally 

 (especially at the ends of the grains, that is, in the direction of the 

 foliation planes) small mica flakes seem to pierce the edge. This 

 appears to indicate that there has been some secondary enlargement. 

 The grains are occasionally composite, but generally homogeneous ; 

 they are rather free from cavities, bubbles or other enclosures, but 

 now and then they enclose microliths, especially of pale-coloured mica. 

 The latter mineral, in like way, is sometimes collected in elongated 

 patches, suggestive of a flaky fragment, sometimes scattered in the 

 ground-mass. The single flakes occur up to about 0*005" in length, 

 but usually are between 0-001" and 0'003' r . As described by one 



* One of these, "which may be either a felspar or one of the andalusites, exhibits 

 roughly parallel lines of dark belonitic enclosures, as described by Professor 

 Bonney (' Quart. Journ. Geol. Soc.,' vol. 45, p. 100). These make an angle of about 

 30° with the general direction of foliation, and are clearly antecedent to it. 



