20 



WESTBURY CLIFF. 



original constituent parts ; very little changed ; in chalk, and all the 

 strata under chalk, the organic remains are, more or less completely, 

 impregnated with mineral matter. The outer crust or shell of many 

 chalk fossils is calcareous, and the internal part filled with flint. In 

 some cases we meet with an internal cast formed in the cavity of a 

 crustaceous animal, and the external covering has disappeared : in 

 other instances, the shell or crust of the animal has formed a mould 

 in the stone, into which mineral matter has been subsequently infilter- 

 ed, and has thus made an external cast. 



It is particularly deserving of attention, that some animal remains 

 contain the most delicate fibres and spines, perfect and unbroken : 

 this proves that the mineral matter in which they are imbedded was 

 deposited in a finely comminuted state, and in a tranquil sea. In 

 some instances the most delicate shells are regularly arranged in the 

 same position in which the animals lived and died, while the animal 

 remains in the strata above or below them, are broken and confusedly 

 aggregated together. The most remarkable instance of this kind 

 1 have ever observed, occurs at Westbury Cliff, on die northern bank 

 of the river Severn, about seven miles below Gloucester. It is a low 

 clifT, nearly perpendicular; the lower part is composed of what is 

 generally called red marie, over which are the lower beds of dark 

 argillaceous limestone and clay, called lias. A few yards above the 

 junction of the lias and red marie, there is a thin stratum of dark 

 micaceous sandstone, entirely filled with bones, and the teeth of the 

 shark, and animals of the saurian or lizard tribe, broken and intermix- 

 ed in the greatest imaginable disorder. Near the upper part of the 

 cliff, not many feet above the stratum filled with bones, there is a thin 

 stratum of whitish argillaceous limestone, called while lias, which is 

 filled with the most delicate minute bivalve shells all arranged in the 

 same position, without any intermixture with shells of other species. 



Facts like these are particularly deserving of the attention of the 

 geologist, as they mark in a striking manner the convulsions which 

 the surface of the globe has, undergone, at different periods. 



The stratum with aggregated bones of saurian animals appears 

 again, on the other side of the Severn, at Aust Passage, where also 

 the junction of the lias and red ground may be observed ; but I could 

 not discover there, any trace of the white lias bed with the bivalves, 

 similar to those at Westbury Cliff. 



Some of the more delicately constructed animals and the fish 

 whose bodies are found entire, imbedded in stone, appear to have 

 been instantaneously destroyed and enveloped in mineral matter, be- 

 fore the putrefactive process could commence.* The process of 



* In the Museum at the Jardin de Plantes in Paris, there is a large specimen 

 of two fossil fish, which are supposed to have been destroyed and covered with 

 mineral matter, when one of them was in the very act of swallowing the other; 

 but an inspection of the specimen inclined me to infer, that the two heads had. 

 been pressed together, by the incumbent weight of stone deposited upon them, 



