242 Mr. Webster on the Strata lying over the Chalk. 



and violent changes, or the action of causes similar to what we per- 

 ceive at the present day. 



And if we reflect upon the manner in which the most delicate 

 recent shells are buried when thrown upon the shore, in the sand 

 and shingles of a beach, without being much mutilated, we shall not 

 fmd it difficult to comprehend how very perfect specimens may 

 sometimes be met with even in our gravel. 



By attending to the revolutions that have happened to these upper 

 strata, this subject will perhaps be less difllicult to understand. Beds 

 of gravel and sand containing fossil shells will be esteemed as the 

 monuments of ancient changes though of different periods. But 

 those shells grouped in families and contained in beds of foliated 

 clay and marl, may be considered as still remaining in their original 

 situations. 



By this distinction we shall be able to separate real alluvial fossils, 

 or such as have been washed out of regular strata from those that 

 have never been disturbed ; and the various states of violent con- 

 vulsion, as well as of quiescence, which the ocean must have ex- 

 perienced during the several eras, the geological history of which 

 we have been considering, are sufficient to account for these ap- 

 pearances. 



In a work lately published by an eminent fossillst, I have met 

 with an opinion, that all the spoils of terrestrial and submarine pro- 

 ductions which we find buried in the strata in this country over the 

 chalk, have been transported from distant climates, and have been 

 deposited in a tumultuous manner by some great convulsion that 

 blended them in one common grave. I should not have thought it 

 necessary to allude to this idea, if I had not understood that it has 

 been considered by some as demonstrating that all the strata over 

 our chalk are alluvial. 



