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The geological inquirer will derive some assistance 

 from the examination of fossil shells, whilst endeavour- 

 ing to ascertain how far the earth contained in the testace- 

 ous and crustaceous coverings of marine animals has con- 

 tributed to the formation of calcareous rocks. It has been 

 conjectured, that besides adding to the bulk of the lime- 

 stone or chalk by the accumulation of their remains still 

 bearing their original forms, that they have also contributed 

 to the surrounding matrix by a solution and subsequent 

 precipitation of the lime which had entered into their 

 composition. If this had been the case, we might expect 

 to find those remains which still bear their original forms, 

 manifesting every degree of resolution, from the slightest 

 influence of the agent in destroying the finest striae to the 

 smoothing of ridges, and even the diminution or removal of 

 projecting points. But nothing of this is discoverable 

 in the fossils of either the flint, the limestone, or the chalk. 

 In the latter, which, by the fineness and purity of its sub- 

 stance, gives strong evidence of its having been depo- 

 sited by precipitation, not the slightest appearance of 

 chemical action on its contained fossil shells is observable. 

 If preserved at all, they are preserved with their sharpest 

 ridges arrd minutest points in the most perfect state. The 

 same is observable not only in the fossil shells of the lime- 

 stone, but in the delicate and beautiful fossils, which have 

 subsequently undergone the change of silicification ; as in 

 the fossils of the Blackdown hills, in Devonshire. 



Shells of alternating Marine and Fresh-water Formations. 

 On examining the crags, the beds of gravel and fossil 

 shells lying over the London clay, numerous fossil shells 

 are found approximating in their characters to the recent 

 shells of our present seas. These, it has been supposed, are 

 the remains of the inhabitants of that sea which covered, at 

 a very distant period, the surface of the planet, and which 



