F. Rutleij — Igneous Rocks of the Warwickshire Coal-field. 559 



but, to have classification, more or less clear definitions must be 

 employed ; without these the whole series of basalts, andesites and 

 diorites may as well be called Greenstones. 



I. Syenitic Eocks. 

 Croft. 1 



Pinkish-grey crystalline rock, resembling a fine-grained granite 

 and apparently composed of pinkish or flesh-coloured felspar, a very 

 little dark mica, quartz, and some dark specks of hornblende and 

 magnetite. Under the microscope the rock is seen to have a holo- 

 crystalline granitic structure, and to consist chiefly of orthoclase 

 and triclinic felspars, quartz, hornblende and magnetite, with pos- 

 sibly a little magnesian mica. The amount of triclinic felspar 

 present renders it necessary to distinguish this rock from an ordinary 

 quartz-syenite. It is an orthoclase-plagioclase syenite, in other 

 words it occupies a position between quartz-syenite and quartz-diorite. 



Croft. 



A pinkish-brown crystalline rock with numerous white, porphyri- 

 tic crystals seldom over one-eighth of an inch in diameter, and small 

 dark greenish-black and black specks. The specimen has a weathered 

 appearance. 



Under the microscope it is seen to consist of orthoclase, a triclinic 

 felspar, which from some of the extinction angles seems to be albite, 

 hornblende in small irregularly developed crystals which are some- 

 times represented by serpentinous pseudomorphs and crystals and 

 irregular grains of magnetite. Quartz occurs plentifully. The rock 

 is essentially a quartz-syenite. It is a more coarsely crystalline 

 rock than the preceding. 



Croft. 



A purplish or reddish-grey, fine-grained crystalline rock, with 

 dark brown spots ranging up to an eighth of an inch in diameter. 



Under the microscope the chief constituents are seen to be 

 felspars, all of which are greatly altered, so that their optical charac- 

 ters afford no clue to the species, quartz, serpentine, apparently 

 pseudomorphous after hornblende, and ilmenite partly converted into 

 leucoxene. 



The rock seems to be a decomposed, fine-grained, quartz-syenite. 



ii. Andesite and Andesitic Tuffs, Caldecote Series. 

 Old tunnel, near Caldecote Hill. 2 Caldecote Series. 



A finely -laminated greenish-brown rock, resembling a fine-grained 

 sandy-mudstone or slate. The specimen is bounded by parallel joint- 

 planes. Under the microscope, with a power of about 75 linear, a 

 considerable proportion of the rock appears between crossed Nicols 

 to consist of isotropic matter finely stippled with very minute doubly 

 refracting granules and traversed by irregular wavy films of a ser- 

 pentinous or sericitic substance, which commonly runs in sinuous 



1 See also " On the Pre- Carboniferous Eoeks of Charnwood Forest," by the Eev. 

 T. G. Bonney and Rev. E. Hill, Q.J.G.S. vol. xxxiv. pp. 119-239, 1878. 



2 See also T. H. Waller, Geol. Mag. 1886, p. 323. 



