498 



MR. E. EUTLET ON" THE ROCKS 



ISTo. 13. Worcestershire Beacon. North side of summit. — A greenish- 

 grey crystalline rock, apparently composed bo a large extent of horn- 

 blende crystals varying from about 2 millim. to smaller dimensions. 

 Under the microscope it is seen to consist of hornblende, decomposed 

 felspars, apatite, and magnetite. The hornblende is very fresh. The 

 cleavages are well defined and the pleochroism strong ; a = brownish- 

 yellow, 6 = dark brownish-green, c— bluish-green. The felspars are 

 in too advanced a stage of decomposition to admit of any determi- 

 nation, but a few of them show faint indications of twin-lamellation. 

 The magnetite occurs in irregular grains (PL XX. fig. 3). 



The rock is possibly a syenite, probably a diorite. The altered 

 condition of the felspar precludes a decided opinion. 



No. 14. Worcestershire Beacon. Summit. — A crystalline rock 

 apparently composed of dark green crystals of hornblende and 

 pinkish-grey felspar. 



Under the microscope the constituents are found to be hornblende, 

 triclinic felspars which show the extinction-angles of labradorite, 

 apatite and magnetite. A little quartz is also present, but it certainly 

 cannot be regarded as an essential constituent of the rock, which is 

 a diorite. The section shows no traces of foliation. It is an erup- 

 tive rock, and its general appearance in situ is that of a vertical 

 dyke about 18 inches to 2 feet broad. 



Portion of a section magnified \ 8 linear is shown in PI. XX. fig. 4, 

 as seen between crossed nicols. 



No. 15. Worcestershire Beacon. North side of summit. — A very 

 fine-grained, pale bluish-grey crystalline rock. Epidote in small 

 grains, triclinic felspar, quartz, and sparsely disseminated grains of 

 magnetite appear, under the microscope, to be the chief constituents 

 of this rock (PI. XX. fig. 5). Here and there a faintly defined linear 

 arrangement of the epidote may be seen, as shown in the drawing, 

 but it can hardly be regarded as foliation. The rock is probably 

 an altered quartz-diorite, but it may, in its present condition, be 

 looked upon almost as epidosite. 



No. 16. Herefordshire Beacon. North side, near top of ancient 

 British Gamp. — A fine-grained crystalline greenish-grey rock with 

 small blackish-green porphyritic crystals. Under the microscope 

 the latter are seen to be hornblende, and ragged fibrous-looking 

 crystals of this mineral appear to constitute a large proportion of 

 the rock and, from their arrangement, to give rise to a wavy and 

 faintly foliated structure (PI. XX. fig. 6). Minute granular crystals 

 of epidote are plentiful, while patches of magnetite, often accom- 

 panied by a little haematite, are common. The remainder of the 

 section appears to consist of felspar, for the most part decomposed. 



Judging from the general appearance of the rock under the 

 microscope, it seems highly probable that it is an altered diabase or 

 andesite tuff ; but it is also possible that the foliation in this, as in 

 some other cases, may be due to shearing. 



No. 17. Herefordshire Beacon. North side, near top of British 

 Camp. — Dark bluish-grey to reddish-brown crystalline rock, show- 



