512 



1TE. F. PXILET OX THE ROCKS 



so examined there may also be some minerals which. I have failed 

 to recognize. Mr. Teall informs me that he has detected sphene in 

 some of the rocks of the North Hill, and I am by no means certain 

 that, in one or two of the sections prepared from specimens collected 

 at the sonthern end of the range, rutile is not present. The opinions 

 frequently expressed concerning the species of the felspars must also 

 be accepted, in some cases, with a certain amount of reserve, since the 

 measurement of the extinction-angles was often made from imperfectly 

 developed crystals in which the directions of the planes of section 

 were extremely doubtful. 



Under any circumstances the paper does but very imperfect 

 justice to the various points discussed in it, and there still remains 

 in these Archaean rocks a vast and comparatively unexplored field 

 for the exercise of the hammer and the microscope. 



EXPLANATION OF THE PLATES. 

 Plate XIX. 



Fig. 1. Gneissic quartz-syenite. North Hill, x 18. (Specimen no. 1.) 



2. Epidote-plagioelase rock. Probably an altered diorite-tuff. North 



Hill. X 18. (Specimen 2.) 



3. Coarsely crystalline and slightly foliated diorite or hornblendic gneiss. 



North Hill. X 18. (Specimen 3.) 



4. Coarsely crystalline quartz-diorite or hornblende-gabbro. X 55. The 



drawing shows portions of crystals of hornblende and orthoclase. 

 (Specimen 4.) 



5. Diorite. Ivy Scar Eock, North Hill. X 25. (Specimen 7.) 



6. Biotite-gneiss. Quarry above church, West Malvern, x 55. (Speci- 



men 9.) 



7. Altered mica-diorite. Large quarry (Leighton's) at mouth of the 



Dingle. X 18. (Specimen 10.) 



8. Granulite. Worcestershire Beacon, near top, north side. X 55, pola- 



rized light, nicols 4-. (Specimen 11.) 



Plate XX. 



Fig. 1. Quartz-syenite or hornblendic granite (feebly foliated ?). Top of North 

 Hill, x 25. (Specimen 6.) 



2. Granite. Worcestershire Beacon, near top, north side. x 18, nicols 



+ . (Specimen 12.) 



3. Diorite ? (syenite ?) (felspars much decomposed). Worcestershire Bea- 



con, top. X 18, nicols -f. (Specimen 13.) 



4. Diorite. Worcestershire Beacon, top (? dyke). X 18, nicols -j-. (Spe- 



cimen 14.) 



5. Epidosite (altered quartz-diorite). Worcestershire Beacon, top, north 



side. X 18. (Specimen 15.) 



6. Diabase-tuff (? foliation clue to pressure-metamorphism). Herefordshire 



Beacon, north side,, near top of ancient British camp. X 25. (Speci- 

 men 16.) 



7. Hornblendic gneiss. Herefordshire Beacon, north side, near top of 



ancient British camp. X 18. (Specimen 17.) 



8. Eucrite or anorthite-basalt. Herefordshire Beacon, close to and on 



west of the cave. X 18. (Specimen 18.) 



9. Basalt. Herefordshire Beacon, east side, at back of the cave. X 5. 



(Specimen 19.) 



j 



