160 S. Allport — On the Midland Basaltic Rocks. 



following constituent minerals — Triclinic felspar, probably Labra- 

 dorite (but which, has not been positively determined), Augite, 

 Titano-ferrite, or magnetic oxide of iron, Olivine, and, very generally, 

 long hexagonal crystals of Apatite. 



In addition to these, the following minerals occur more or less 

 frequently, as secondarj'- formations filling cavities ; Calcite, a brown 

 Zeolite, and a green chloritic mineral ; the latter sometimes filling, 

 at others merely lining, the minute cavities, the central portion in 

 this case being Calcite. 



The felspar usually occurs iu rather long prisms, showing the 

 characteristic striae when viewed by polarised light ; the augite is 

 frequently well crystallized, and contains many glass-cavities ; the 

 iron oxide occurs in minute grains, or as thin plates ; and the Olivine 

 as crystals or irregular grains. As stated in my previous communi- 

 cation, the Olivine almost invariably occurs as a pseudomorph ; there 

 is, however, no difficulty in detecting it, as it frequently relains the 

 characteristic crystalline form, and, even when in irregular grains, 

 the peculiar veined appearance, and irregular play of colours when 

 examined by polarized light, are decisive as to its character. I have, 

 however, been again successful in finding specimens containing the 

 mineral in various stages of alteration. 



In South Staffordshire the igneous rocks present two varieties ; one 

 is a hard greyish-black basaltic rock, with a conchoidal fracture, 

 sometimes perfectly columnar, as at Pouk Hill, near Walsall ; the 

 other is locally known as " Green rock," and differs only from the 

 former in that it contains a larger proportion of a green chloritic 

 mineral, which is evidently a secondary formation. It is a clear green 

 when fresh broken, but turns blackish on exposure. This " Green 

 rock" occurs in sheets between the Coal-measures, and has imder- 

 gone a greater amount of alteration than the more massive portions 

 of the rock ; usually it is not so hard, and Carbonate of Lime and 

 Zeolites are more frequent. 



The rock from Coalville presents precisely the same characters, 

 and is especially interesting, as it contains Olivine in different 

 stages of alteration. In this locality the basalt lies on the upper 

 seam of coal, which is said to be altered ; it is itself covered by un- 

 disturbed and unaltered new Eed Sandstone. 



The mass of " Basalt" at Little Wenlock, three miles south of 

 Wellington, is also precisely of the same character ; a thin section 

 shows several pseudomorphs after 01i\dne, in some of which the 

 change is not complete ; and also examples of the chloritic mineral 

 filling up spaces between the crystals of felspar and augite. 



The rock in Arley Wood near Shatterford is a fine grained black 

 basaltic rock, a section of which contains a perfectly-formed crystal 

 of altered Olivine. 



The " Basalt" capping the Titterstone Clee Hill, contains Olivine 

 nearly unaltered, and well formed crystals of Augite. This rock is 

 quite undistinguishable from specimens from Eowley. 



The well-known Toadstone of Derbyshire is an amj^gdaloidal 

 variety of the same kind of rock ; it is regularly interbedded with the 



