26 Prof. BucKLAND and Mr. De la Beche on the 



sandy loam beds of this formation afford an useful brick earth. The passage 

 of the lowest strata into Oxford clay is indicated by the presence of the Gri/- 

 phcea dilatata in the beds of grit, and this passage is analogous to that which 

 occurs at Heddington Hill near Oxford ; but the presence of an upper cal- 

 careous grit and gradual passage of the superior strata at Weymouth into 

 Kimmeridge clay, show a more perfect development of this part of the oolite 

 formation in Dorset than in Oxfordshire. In the sections at Heddington the 

 upper grit is wanting, and the Kimmeridge clay reposes immediately on 

 the oolitic building-stone : the surface of this stone is also guttered over and 

 furrowed with water-worn cavities and small rock-basins, marking a destruc- 

 tive action of the sea before the deposition of the Kimmeridge clay : this 

 water-worn surface of the oolite is also decomposed and become rusty to the 

 depth of about a foot, in a manner unusual where the series of depositions 

 has been regularly continuous, and its decomposition seems to have resulted 

 from long exposure to water before the laying on of the Kimmeridge clay. 

 These circumstances are duly noticed by Conybeare and Phillips*. 



All the beds of the Oxford oolite formation near Weymouth are loaded 

 with shells similar to those found in the same formation in Wiltshire, Oxford- 



* Outlines of the Geology of England and Wales, p. 189, note. 



Prof. Sedgwick, in his comparison of the appearance of the coral rag formation near Scar- 

 borougli and Weymouth with that of Oxford (Ann. of Phil., May 182G), conjectures that the 

 upper portions of the Scarborough and Weymouth sections may be wanting near Oxford, and that 

 the coral rag and freestone of Heddington together, represent the central group of the Weymouth 

 and Steeple Ashton sections : thus, at its two extremities in the coast of Dorset and Yorkshire, 

 the superior members of tliis formation are most fully developed, whilst they are wanting, and 

 have been apparently removed from the central part of their range near Oxford. We entirely 

 agree with Prof. Sedgwick in these remarks, and in the consequences which he draws as to 

 the imperfection of the type of this formation near Oxford : the whole of this subject has 

 been fully illustrated by Mr. Phillips in his excellent work on the Coast of Yorkshire, and still 

 more recently by Mr. Lonsdale in his valuable paper on the Oolite District near Bath (GeoL 

 Trans, vol. iii. Part II. p. 262), in which he gives a section of the Oxford oolite formation at 

 Highworth, where the upper members are represented by about seven feet of alternating beds of 

 sand and rubbly oolite, or oolitic calcareous grit : he also shows that near Steeple Ashton the 

 superior beds appear under the form of ten feet of sand, resting on ten feet of ferruginous clay 

 interspersed with oolitic grains of hydrate of iron. Some bones of a Plesiosaurus have been found 

 in this clay by Mr. Mead. 



According to M. de Caumont, a similar alternation of strata of sand and calcareous sandstone, 

 with beds of clay and of imperfect oolitic limestone, affords, on the coast of Normandy, a group 

 corresponding with the upper calcareous grits of Weymouth and the coast of Yorkshire, interposed 

 between the Kimmeridge clay and tlie coral rag. (See M. de Caumont's Sectional Lists of the 

 Cliff at Hennequeville ; of the Hillof Glos near Lisieux ; and of St. Julien-sur-Calone near Pont 

 I'Eveque. pp. 113, 114,115.) 



