454 



and Oake near Taunton ; the latter have supplied the freestone used 

 in the towers and bridges at the town of Taunton. 



In the cliffs at Oreham, two miles E. of Exmouth, there are beds 

 of sandstone, probably referrible to the Keiiper formation, which have 

 supplied the olive-coloured sandstone of which the cathedral of Exeter 

 is built ; and at Pyle, in Glamorganshire, a few miles E. of Neath, a 

 valuable building-stone lately employed in constructing the castle of 

 Margum, is obtained from strata, which the author also refers to the 

 Keuper-sandstone of Germany. 



Mr. Murchison has noticed Keuper-sandstone in several localities 

 in Gloucestershire and Worcestershire, near Tewkesbury and Ne- 

 vi^ent. 



A paper "On the Geological Structure and Phenomena of the north- 

 ern part of the Cotentin, and particularly of the immediate vicinity 

 of Cherbourg," by the Rev. W. B. Clarke, F.G.S., was then read. 



In an account of the Cotentin published in the 35th volume of 

 the Journal des Mines, M. Alexander Brongniart gives a full account 

 of the limestone, slates, quartz rock and syenite or granite com- 

 posing the country; but the chief object of that memoir is to prove 

 the comparatively recent origin of the granitic rocks. 



Mr. Clarke, in detailing the characters of the formations follows 

 closely the account of M. Brongniart, and adopts fully the views of 

 that geologist respecting the age of the granite. He also quotes 

 Prof Sedgwick's observations on the comparatively recent origin of the 

 granite of Cornwall, and the adjacent portion of Devonshire; and 

 points out the general agreement in structure of that district with 

 the Cotentin. 



The country near Cherbourg consists of hills, and ridges of quartz 

 rock alternating with valleys of slate, occasionally associated with 

 syenite and greenstone, under circumstances which lead to the con- 

 clusion that the igneous formations are of posterior origin. 



The quartz rock varies in colour and hardness, seldom assumes an 

 arenaceous character, and the fracture is sometimes vitreous. The 

 beds are generally inclined at a considerable angle, the dip changing 

 in different localities. 



The slates vary greatly in their characters, being sometimes argil- 

 laceous, at others talcose, and occasionally assume a form called by 

 M. Brongniart steaschiste noduleux which has a base of green golssy 

 slate inclosing nodules of quartz. 



The slates and the quartz rock alternate frequently, and pass into 

 each other by insensible gradations. 



The quartz rock splits naturally into irregular masses, which have 

 nevertheless some of the angles of fixed dimensions viz. 103°, 64°, 

 and 83°. These measurements Mr. Clarke has been enabled to obtain 

 in some instances, by producing two sides, which in the specimens 

 were cut off by the intersection of a third plane. On measuring frag- 

 ments of the green variety of schist, he found the same angles under 

 the same circumstances of position, proving that similar causes had 

 acte<l on the two formations en masse ; the same sets of joints, 

 bedding lines, and cleavage, being found in each formation. 



