564 F. Rutley — Igneous Rocks of the Warwickshire Coal-field. 



stance being probably pseudomorpbous after olivine. A few fan- 

 like or divergent groups of capillary crystals occur bere and tbere in 

 tbe section. Tbey undergo extinction approximately parallel to the 

 longest axes of the minute rods, and are probably epidote. The 

 magnetite occurs in irregularly-shaped grains and in well-developed 

 octahedra. A little hornblende may be present, but the evidence for 

 this is not satisfactory. The rock is a diabase. 



Stockingford Cutting, Midland Eailway (E. of bridge). Intrusive 

 in Lower Silurian Shales. 



A very fine-grained, greenish-grey crystalline rock, containing 

 small spots and very numerous minute specks of pyrites. The rock 

 effervesces freely when touched with acid. 



Under the microscope it is seen to consist of triclinic felspar 

 (labradorite), serpentine often in pseudomorphs after olivine, horn- 

 blende, pyrites, calcite, and specks of a yellowish white substance, 

 either kaolin or leucoxene, but probably the former. It is difficult 

 to say whether this rock is to be regarded as a basalt or a diorite. 

 The occurrence of olivine in dioritic rocks from this neighbourhood 

 has already been noticed by Mr. S. Allport. 1 



Midland Eailway, Stockingford Cutting, Nuneaton. Upper surface 

 of dyke intrusive in Lower Silurian Shales. 



A very fine-grained greenish-grey or drab-coloured crystalline 

 rock, showing numerous minute specks of pyrites. 



Under the microscope the constituents appear to be chiefly triclinic 

 felspar, serpentine pseudomorphous after hornblende, a very little 

 unaltered hornblende and a considerable quantity of pyrites, some 

 of which occurs in triangular sections which give angles of approxi- 

 mately 110° (the angle formed by the edges of an octahedron). It 

 therefore seems pi'obable that the pyrites in this case is pseudo- 

 morphous after magnetite, and this appears the more likely since no 

 magnetite is visible in the section, although the rock is one in which 

 this mineral is generally present. So far as I am aware, pseudo- 

 morphs of pyrites after magnetite are of very unusual occurrence, 

 but instances are quoted by Delesse. 2 The rock is a diorite. 



Oldbury Eeservoir. Very thick sheet intrusive in Lower Silurian 



Shales. 



A greenish-grey crystalline rock, spotted with numerous dark- 

 green or blackish crystals of hornblende. It also shows many 

 specks of pyrites and the joint planes are coated with calc-spar. 



Under the microscope the rock is seen to be composed of triclinic 

 felspar, crystals of hornblende, larger than those seen in the rocks 

 already described, and exhibiting the interrupted crystallization, 

 sometimes termed ophitic, a considerable quantity of kaolin, specks 

 of pyrites and also a little calcite. The rock is a diorite. 



1 Quart. Journ. Geol. Soc. vol. xxxv. p. 639. 



2 llecherches sur les Pseudoniorpkoses, Tableau II. p. 52, Annales des Mines, 

 t. xvi. 1859. 



