246 Mr. Webster on the Strata lyitig over the Chalk. 



that seem to have had considerable influence upon organic life. 

 The almost entire absence in the lower beds of those siliceous 

 nodules that are so numerous in the upper one, and the remarkable 

 differences in their animal remains, furnish sufficient reasons for this 

 supposition. 



Calcareous, argillaceous and siliceous matter, the whole or a part 

 of which was in a state of solution, originally formed the mass of 

 this formation. Of these the argillaceous seems to have subsided 

 first, but more or less mixed with calcareous earth. The silex now 

 occupies the upper division, but whether separated by the action of 

 chemical affinities, or introduced subsequently, does not yet appear. 

 The tranquil state of the ocean during this period may be inferred 

 from the perfect preservation of the numerous delicate fossil organic 

 bodies now found in the chalk. 



An era of turbulence seems to have succeeded ; during which 

 howeA'^er the depositions of the plastic clay and sand denote certain 

 intervals of repose. The surface of the chalk already solidified was 

 in a certain degree, though irregularly, subjected to the agency of 

 water in motion ; and other causes might have combined in 

 destroying the original horizontality of its position. But where the 

 vast bed of London clay subsided, the sea must have regained its 

 former tranquility. 



The numerous vestiges of vegetables as well as of animals to be 

 found in this stratum, whose recent analogues are now seen only 

 in tropical countries, involuntarily leads the mind to contemplate 

 w'ith wonder the altered condition of this portion of the globe. 

 Have the laws which regulate the place and motions of this earth 

 in the system of the universe been subjected to change? Are there 

 in these any sources of irregularity or gradual alteration, the proofs 

 of which can be detected ? these are questions for astronomers. 



