401 



arranged in directions parallel to the tabular masses of green roof- 

 ing slate ; but pass themselves into a slaty texture with a strike and 

 dip parallel to those of the true roofing slate. They also pass into 

 brecciated masses similar to those which form a part of the slate 

 groups. From these facts, — as well as from the negative facts, that 

 the porphyries never penetrate the roofing slate in the form of dykes, 

 and produce no mineral change in the limestone beds resting on 

 them, — it is inferred that the whole group is of one formation, which 

 has originated in the simultaneous action of aqueous and igneous 

 causes long continued. 



§ 3. Skiddaw slate. — The author briefly describes the range and 

 extent of this group, its position below the preceding, and some of 

 its mineral changes from fine, glossy, clay-slate, much penetrated by 

 quartz veins, into, though rarely, very coarse greywacke. It does not 

 generally effervesce with acids, and contains no organic remains : it 

 is chiefly distinguished from the first group above described, by these 

 negative properties, and by its being of finer texture. 



§ 4. — Crystalline slaty rocks in the central portions of Skiddaw 

 Forest, immediately between the preceding group and the central 

 granite. 



This group is described as being irregular in its order and ill 

 exposed, but from the comparison of a series of sections appears to 

 be separable into the following subdivisions. 



(1.) Skiddaw slate with interspersed crystals of chiastolite, alter- 

 nating with and passing into the preceding group. 



(2.) A similar slate with numerous crystals of chiastolite, passing 

 in the descending order into a crystalline slate sometimes almost 

 composed of matted crystals of chiastolite. 



(3.) Mica slate spotted with chiastolite. 



(4.) Quartzose and micaceous slates sometimes passing into the 

 character of gneiss. 



With this group the paper terminates: but the author promises to 

 resume the subject, and describe, in order, first the several unstratified 

 masses above enumerated; and then the changes produced by the 

 protrusion of the unstratified masses, both on the position and mineral 

 character of the several stratified groups. 



May 30 th. — A paper was first read "On the Basalt of the Titterstone 

 Clee Hill, Shropshire," being the concluding part of a memoir on the 

 Ludlow district, laid before the Society on the 29th of February, by 

 J. Robinson Wright, Esq., F.G.S. employed on the Ordnance Trigo- 

 nometrical Survey. 



The basalt occupies the two highest points of the hill, called the 

 Giant's Chair and the Hoar Edge, which are separated from each 

 other by a narrow ravine. It rests partly upon the old red sandstone, 

 and partly upon the coal measures; and occasionally assumes a 

 columnar structure, — the prisms inclining at an angle of 75°. Be- 

 sides these overlying masses a basaltic dyke has been ascertained to 

 cut through and greatly affect the coal measures ; and the author 

 suggests that the outburst of this dyke may, from its direction, possibly 

 form the north-westerly escarpment of the Hoar Edge. 



