280 The Rev. W. Buckland on the Plastic Clay Formation. 



An appearance somewhat analogous is noted by M. M. Cuvier and 

 Brongniart (Essai sur la Geog. Min- des Environs de Paris, p. 17,) 

 in a coarse variety of the French plastic clay which immediately 

 covers the chalk at Meudon ; where a breccia composed of frag- 

 ments of chalk imbedded in a kind of argillaceous paste has filled 

 the fissures and irregularities -which existed on the surface of the 

 subjacent chalk before the deposition of the plastic clay. 



The same thing may be seen on a small scale in the chalk pit at 

 Woolwich, where there are fissures extending some feet downwards 

 into the body of the chalk, varying in breadth from an inch to more 

 than a foot, and sometimes spreading laterally so as to form con- 

 siderable cavities, which together with the fissures are filled with 

 sand that has been introduced from the incumbent stratum. 



At Reading the chalk is quarried below the green sand contain- 

 ing oysters (No. 2) to the depth of about 25 feet, when the work- 

 ings are stopped by water at a point nearly on a line with the leve 

 of the river Kennet, below which there can be no discharge of 

 water from the chalk, through the medium of the neighbouring 

 springs. In this thickness of 25 feet of chalk, there is but one re- 

 gular and continuous course of flints, and in this they are dis- 

 posed in tabular masses, for the most part of about two inches in 

 thickness. (This bed is but a few feet above the water). In the 

 chalk that lies above this siliceous stratum, the flints are disposed 

 irregularly with their usual characters and eccentric forms, derived, 

 in many instances, from the organic remains which they envelope. 

 They are collected for the use of the porcelain manufactories. The 

 chalk itself is extracted largely from under the sands and clays, by 

 means of shafts and levels, to be burnt into lime. There are no 

 septaria or concretions in any of the strata above the chalk, nor 

 the smallest traces of animal or vegetable remains, excepting in the 



