Geology of the Neighbourhood of Weymouth, ^c. 



25 



so. Oolitic grit, — Trochus.Pecten — three beds 

 alternating with marl. 



31. Brown, reddish grit — oysters abundant, — 



Pectines, Ammonites, Gryphcea dilataia, 

 G. hullata ? Trigonise. 



32. Yellow brown, sandy grit, forty feet, — 



Grypht^a dilatata, oysters, sharp-keeled 

 Ammonite, other Ammonites, Pectines, 

 Nautili: the hard beds contain concre- 

 tions resembling a mass of entangled 



stems of Alcyonia. Prof. Sedgwick has 

 shown the resemblance of these beds to 

 those of the same formation near P'iley 

 Bridge and Scarborough Castle, where 

 the sandstone is similarly aggregated into 

 irregularly branching cylindrical concre- 

 tions. 

 33. Oxford clay, abounding in Gryphcea dila- 

 tata. 



It appears from this section, that the Oxford oolite formation is composed 

 of alternations of imperfectly oolitic limestone and calcareous grit, with nume- 

 rous partings of clay. The superior beds are loose and sandy, and may be 

 considered analogous to the upper calcareous grit in Yorkshire, described by 

 Mr. Phillips; they are best seen near Sandsfoot Castle, where the uppermost 

 of them contain deltoid oysters, and become gradually more argillaceous until 

 they pass into Kimmeridge clay : the central beds are the most oolitic, some- 

 times loose and sandy, and at other times compact and in continuous beds : they 

 are most oolitic at the village of Wyke Regis and in the cliffs near Osmington, 

 at both which places they afford a light-coloured building-stone, which, but 

 for the vicinity of Portland, might have been applied to purposes of architec- 

 ture. In the cliffs west of Wyke Regis, they show the same oblique cleavage 



which is so common in oolitic strata. Thus j^.. , 



M. Boblaye, in his paper on the Jura \\/\\\\^\\\\ 



Formation in the North of Prance*, no- ^^^^^^ 



tices that in the great oolitic quarries of Ballon near Stenay, lines of false 

 division cross the true stratification at angles of 43° or 50°. Examples of the 

 same kind are seen in the Oxford oolite quarries at Heddington, and in the 

 forest marble and great oolite along the road from Cirencester to Bath ; 

 similar partings occur also in the new red sandstone at Bridgenorth, but in 

 a manner much more complicated, and crossing the true strata in all possible 

 directions. 



Beneath these central oolitic beds, strata of semi-calcareous sand and cal- 

 careous grit prevail, and display alternations of sand and sandy loam, with 

 continuous beds of calcareous grit and beds of large concretions lodged in 

 strata of sand. The entire thickness of these calcareous grit beds with their 

 largest concretions, is best exhibited in Ham Cliff, about three miles north- 

 east of Weymouthf . In the hill immediately on the west of Weymouth, the 



* Ann. dcs Scien. Nat., Mai 1829. 

 VOL. IV. SECOND SERIES. 



t See Plate II. fig. 8. 



